Andy McFadden's
CD-Recordable FAQ - Section 7

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Last-modified: 2010/01/09
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[7] Media
[7-1] What kinds of media are there?
[7-2] Does the media matter?
[7-3] Who manufactures CD-R media?
[7-4] Which kind of media should I use?
[7-4-1] What's the best brand of media?
[7-5] How long do CD-Rs and CD-RWs last?
[7-6] How much data can they hold? 650MB? 680MB?
[7-7] Is it okay to write on or stick a label on a disc?
[7-7-1] Can I write on them? What kind of pen should I use?
[7-7-2] Are labels okay?
[7-8] How do CD-Rs behave when microwaved?
[7-9] What can I do with CD-R discs that failed during writing?
[7-10] Where can I find jewel cases and CD sleeves?
[7-11] What's "unbranded" CD-R media?
[7-12] How do I repair a scratched CD?
[7-13] What's this about a Canadian CD-R tax?
[7-14] Can I get 80mm (3-inch "cd single") CD-Rs?
[7-15] Where can I find CD-ROM business cards and "shaped" CDs?
[7-16] Can you tell pressed CDs and silver CD-Rs apart?
[7-17] What's the difference between "data" and "music" blanks?
[7-18] How do I convert data CD-Rs into "consumer audio" blanks?
[7-19] Is translucent media bad?
[7-20] How do I destroy CD-R media beyond all hope of recovery?
[7-21] Can I recycle old CDs, CD-Rs, and CD-RWs?
[7-22] Is there really a fungus that eats CDs?
[7-23] How do I clean CD-R and CD-RW discs?
[7-24] Are "black" discs different from other discs?
[7-25] My disc just shattered in the CD drive!
[7-26] How do I tell which side on a silver/silver disc is up?
[7-27] How should I handle and store CDs?
[7-28] What causes the rainbow effect when looking at the data side?
[7-29] Can I print directly on a CD-R?

Subject: [7] Media

This section covers recordable CD media.

Subject: [7-1] What kinds of media are there?

The basic building blocks of CD-R media are organic dye and a reflective layer. The dye types currently in use are:

In addition, Kodak has patented a "formazan" dye, which is light green. This has been reported to be a hybrid of cyanine and phthalocyanine.

The reflective layer is either a silver alloy, the exact composition of which is proprietary, or 24K gold. Aluminum isn't used in CD-R media because the metal reacts with the dyes.

Discs come in many different colors. The color you see is determined by the color of the reflective layer (gold or silver) and the color of the dye (light blue, dark blue, green, or colorless). For example, combining a gold reflective layer with cyanine (blue) dye results in a disc that is gold on the label side and green on the writing side.

Many people have jumped to the conclusion that "silver" discs are made with pure silver, and have attempted to speculate on the relative reflectivity and lifespan of the media based on that assumption. According to one source, silver is susceptible to corrosion when exposed to sulfur dioxide (a common air pollutant), so manufacturers use alloys of silver to inhibit corrosion.

Taiyo Yuden produced the original gold/green CDs, which were used during the development of CD-R standards. Mitsui Toatsu Chemicals invented the process for gold/gold CDs. Mitsubishi's NCC subsidiary developed the metalized azo dye. Silver/blue CD-Rs, manufactured with a process patented by Verbatim, first became widely available in 1996. According to the Ricoh web site, the silver/silver "Platinum" discs, based on "advanced phthalocyanine dye", were introduced by them in 1997. They didn't really appear on the market until mid-1998 though. Kodak Japan holds the patent on formazan dye.

One reason why there are multiple formulations is that the materials and processes for each are patented. If a new vendor wants to get into the CD-R market, they have to come up with a new combination of materials that conforms to the Orange Book specifications.

Some CDs have an extra coating (e.g. Kodak's "Infoguard") that makes the CD more scratch-resistant, but doesn't affect the way information is stored. The top (label) side of the CD is the part to be most concerned about, since that's where the data lives, and it's easy to damage on a CD-R. Applying a full circular CD label will help prevent scratches.

An EMedia Professional article discussing the composition of the newer discs is online at

CD-RW discs have an entirely different composition. The data side (opposite the label side) is a dark silvery gray that is difficult to describe.

Subject: [7-2] Does the media matter?

Yes. There are four factors to consider:

  1. Does it work with your recorder?
  2. Which CD readers can use it?
  3. How long does it last before it starts to decay?
  4. What's the typical BLER (BLock Error Rate) for the media?
Some audio CD players (like the ones you'd find in a car stereo) have worked successfully with one brand of media but not another. There's no "best" kind, other than what works the best for you.

Some people have found brand X CD-R units work well with media type Y, while other people with the same unit have had different results. Recording a disc at 4x may make it unreadable on some drives, even though a disc recorded at 2x on the same drive works fine.

To top it all off, someone observed that discs burned with one brand of CD-R weren't readable in cheap CD-ROM drives, even though the same kind of media burned in a different device worked fine. The performance of any piece of media is always a combination of the disc, the drive that recorded it, and the drive that reads it.

A number of specific discoveries have been posted to Usenet, but none of them are conclusive. Many people have reported that Kenwood CD players don't deal with CD-Rs very well, while Alpine units play nearly everything. However, things change as product lines evolve over time.

Some users have found that the *quality* of audio recordings can vary depending on the media. Whatever the case, if you find that CD-Rs don't sound as good as the originals, it's worthwhile to try a different kind of media or a different player. See section (4-18) for other ideas.

If you want to see what media test results look like, take a look at

One final comment: while there are clearly defined standards for CD-R media, there are no such standards for CD and CD-ROM drives -- other than that they be able to read CDs. It is possible for media to be within allowed tolerances, but be unreadable by a CD-ROM drive that can handle pressed discs without trouble. All you can do in this sort of situation is find a better-quality CD or CD-ROM drive, or switch to a brand of media whose characteristics are on the other side of the tolerance zone.

Subject: [7-3] Who manufactures CD-R media?

Taiyo Yuden made the first "green" CDs. They are now manufactured by TDK, Ricoh, Kodak, and probably several others as well.

Mitsui Toatsu Chemicals (MTC) made the first "gold" CDs. They are now manufactured by Kodak and possibly others as well.

Verbatim made the first "silver/blue" CDs.

Most CD-R brands (e.g. Yamaha and Sony) are actually made by a handful of major disc manufacturers. Attempting to keep track of who makes what is a difficult proposition at best, since new manufacturing plants are being built, and resellers can switch vendors. See section (2-33) for notes about identifying the source of a CD-R.

Subject: [7-4] Which kind of media should I use?

There is no "best" media for all recorders. You can't tell how well a disc will work just by looking at it; the only way to know is to put it in *your* recorder, write a disc, then put it in *your* reader and try it. Statements to the effect that "dark green" is better than "light green" are absurd. Some discs are more translucent than others, but that doesn't matter: they only have to reflect light in the 780nm wavelength, not the entire visible spectrum. See (7-19).

It's probably a good idea to start by selecting media that is certified for your recorder's desired write speed. See section (3-31) for some other remarks about recording speed.

Speed considerations are more important for CD-RW than CD-R. Many drives refuse to record at speeds higher than the disc is rated for. On top of that, there are "ultra speed +" blanks (for 32x recording), "ultra speed" blanks (for 8x-24x), "high speed" blanks (for 4x-10x) and "standard" blanks (for 1x-4x). The faster blanks are labeled with a "High Speed CD-RW" or "Ultra Speed CD-RW" logo, and will not work in older drives.

The Orange Book standard was written based on the original "green" cyanine discs from Taiyo Yuden. Cyanine dye is more forgiving of marginal read/write power variations than "gold" phthalocyanine dye, making them easier to read on some drives. On the other hand, phthalocyanine is less sensitive to sunlight and UV radiation, suggesting that they would last longer under adverse conditions.

Manufacturers of phthalocyanine-based media claim it has a longer lifespan and will work better in higher speed recording than cyanine discs. See for some notes on low-level differences between media types.

There is no advantage to using expensive "audio CD-Rs" or "music blanks". There is no difference in quality between consumer audio blanks and standard blanks from a given manufacturer. If you have a consumer audio CD recorder, you simply have no other choice. There is no way to "convert" a standard blank into a consumer audio blank. See section (5-12) for notes on how you can trick certain recorders into accepting standard blanks.

Trying samples of blanks is strongly recommended before you make a major purchase. Remember to try them in your reader as well as your writer; they may not be so useful if you can't read them in your normal CD-ROM drive.

Maxell's CD-R media earned a miserable reputation on Usenet. In April '97 Maxell announced reformulated media that seemed to work better than the previous ones. It appears they may no longer make their own media.

Some good technical information is available from In particular, "Are green CD-R discs better than gold or blue ones?" at

BLER measurements for a variety of recorders and media is in a big table on

See also "Is There a CD-R Media Problem?" by Katherine Cochrane, originally published in the Feb '96 issue of CD-ROM Professional.

Subject: [7-4-1] What's the best brand of media?

As noted in (7-4), there is no guarantee that brand X will be the absolute best in recorder Y. However, some brands are recommended more often than others. It does pay to be brand-conscious.

Brands most often recommended: Mitsui, Kodak, Taiyo Yuden, and TDK. Sometimes Pioneer and Ricoh. It appears that HP, Philips, Sony, Yamaha, and Fuji use these manufacturers for most of their disks. (Kodak no longer manufactures media.)

Brands that are often trashed: Maxell, Verbatim, Memorex, Ritek, Hotan, Princo, Gigastorage, Lead Data, Fornet, CMC Magnetics. Many "no-name" bulk CD-Rs are one of these brands.

Sometimes a particular line of discs from a particular manufacturer or reseller will be better than others from the same company. For example, Verbatim DataLifePlus discs are recognized as pretty good, but Verbatim ValuLife are seen as being of much lower quality.

Sometimes company names change. For example, in June 2003 Mitsui Advanced Media was purchased from Mitsui Chemicals by Computer Support Italcard (CSI) of Italy to form MAM-A, Inc.

The country of manufacture may also be significant. Some manufacturers maintain plants in different countries, and don't always maintain the same level of quality.

In humid tropical climates, care must be taken to find discs that stand up to the weather. One user reported that the data layer on Sony CDQ 74CN discs began cracking after a couple of months in an otherwise sheltered environment (e.g. no direct sunlight). Mitsubishi CD-R 700 and Melody 80 Platinum discs fared much better.

Subject: [7-5] How long do CD-Rs and CD-RWs last?

CD-RWs are expected to last about 25 years under ideal conditions (i.e. you write it once and then leave it alone). Repeated rewrites will accelerate this. In general, CD-RW media isn't recommended for long-term backups or archives of valuable data.

The rest of this section applies to CD-R.

The manufacturers claim 75 years (cyanine dye, used in "green" discs), 100 years (phthalocyanine dye, used in "gold" discs), or even 200 years ("advanced" phthalocyanine dye, used in "platinum" discs) once the disc has been written. The shelf life of an unrecorded disc has been estimated at between 5 and 10 years. There is no standard agreed-upon way to test discs for lifetime viability. Accelerated aging tests have been done, but they may not provide a meaningful analogue to real-world aging.

Exposing the disc to excessive heat, humidity, or to direct sunlight will greatly reduce the lifetime. In general, CD-Rs are far less tolerant of environmental conditions than pressed CDs, and should be treated with greater care. The easiest way to make a CD-R unusable is to scratch the top surface. Find a CD-R you don't want anymore, and try to scratch the top (label side) with your fingernail, a ballpoint pen, a paper clip, and anything else you have handy. The results may surprise you.

Keep them in a cool, dark, dry place, and they will probably live longer than you do (emphasis on "probably"). Some newsgroup reports have complained of discs becoming unreadable in as little as three years, but without knowing how the discs were handled and stored such anecdotes are useless. Try to keep a little perspective on the situation: a disc that degrades very little over 100 years is useless if it can't be read in your CD-ROM drive today.

One user reported that very inexpensive CD-Rs deteriorated in a mere six weeks, despite careful storage. Some discs are better than others.

An interesting article by Fred Langa (of on describes how to detect bad discs, and discusses whether putting an adhesive label on the disc causes them to fail more quickly.

By some estimates, pressed CD-ROMs may only last for 10 to 25 years, because the aluminum reflective layer starts to corrode after a while.

One user was told by Blaupunkt that CD-R discs shouldn't be left in car CD players, because if it gets too hot in the car the CD-R will emit a gas that can blind the laser optics. However, CD-Rs are constructed much the same way and with mostly the same materials as pressed CDs, and the temperatures required to cause such an emission from the materials that are exposed would melt much of the car's interior. The dye layer is sealed into the disc, and should not present any danger to drive optics even if overheated. Even so, leaving a CD-R in a hot car isn't good for the disc, and will probably shorten its useful life.

See also, especially about some inaccurate reporting in the news media.

See "Do gold CD-R discs have better longevity than green discs?" on

There's a very readable discussion of CD-R media error testing on that leaves you with a numb sense of amazement that CD-Rs work at all. It also explains the errors that come out of MSCDEX and what the dreaded E32 error means to a CD stamper.

An interesting document entitled "Care and Handling of CDs and DVDs - A Guide for Librarians and Archivists" can be found on the web sites for the National Institute of Standards and Technology (NIST) and the Council on Library and Information Resources (CLIR). View it on the web at or as a PDF from It has a wealth of information about disc composition and longevity, as well as recommendations for extending the lifespan of your media.

Another good NIST article, "Stability Comparison of Recordable Optical Discs -- A Study of Error Rates in Harsh Conditions" can be found at

Kodak has some interesting information about their "Ultima" media. See, specifically the "KODAK Ultima Lifetime Discussion" and "KODAK Ultima Lifetime Calculation" white papers (currently in PDF format). The last page discusses the Arrhenius equation, which is used in chemistry to calculate the effect of temperature on reaction rates. The Kodak page defines it as:

t = A * exp(E/kT)
where 'exp()' indicates exponentiation. 't' is disc lifetime, 'A' is a time constant, 'E' is activation energy, 'k' is Boltzmann's constant, and 'T' is absolute temperature. The equation allows lifetime determined at one temperature to be used to establish the lifetime at another. If a disc breaks down in three months in extreme heat, you can extrapolate the lifetime at room temperature.

The trouble with the equation is that you have to know either 'A' or 'E'. It appears that 'A' can be estimated based on empirical evidence, but see for some cautions about how tricky it can be to choose the right value.

Subject: [7-6] How much data can they hold? 650MB? 680MB?

There are 21-minute (80mm/3-inch), 74-minute, 80-minute, 90-minute, and 99-minute CD-Rs. These translate into data storage capacities of 184MB, 650MB, 700MB, 790MB, and 870MB respectively (see below for exact figures). See section (7-14) for more about 80mm CD-Rs, and sections (3-8-1) and (3-8-2) for notes on 80-, 90-, and 99-minute blanks. There used to be 63-minute CD-Rs, but these have largely vanished.

Typical 74-minute CD-Rs are advertised as holding 650MB, 680MB, or even 700MB of data. The reality is that they're all about the same size, and while you may get as much as an extra minute or two depending on the exact construction, you're not usually going to get an extra 30MB out of a disc labeled as 74-minute media. See section (3-8-3) for information on writing beyond a disc's stated capacity.

Folks interested in "doing the math" should note that only 2048 bytes of each 2352-byte sector is used for data on typical (Mode 1) discs. The rest is used for error correction and miscellaneous fields. This is why you can fit 747MB of audio WAV files onto a disc that holds 650MB of data.

It should also be noted that hard drive manufacturers don't measure megabytes in the same way that RAM manufacturers do. The "MB" for RAM means 1024x1024, but for hard drives it means 1000x1000. A data CD that can hold 650 "RAM" MB of data holds about 682 "disk" MB of data, which is why many CD-Rs are mislabeled as having a 680MB capacity. (The notion of "unformatted capacity" is a nonsensical myth stemming from early hard drives.)

Spelled out simply:

21 minutes == 94,500 sectors == 184.6MB CD-ROM == 212.0MB CD-DA
63 minutes == 283,500 sectors == 553.7MB CD-ROM == 635.9MB CD-DA
74 minutes == 333,000 sectors == 650.3MB CD-ROM == 746.9MB CD-DA
80 minutes == 360,000 sectors == 703.1MB CD-ROM == 807.4MB CD-DA
90 minutes == 405,000 sectors == 791.0MB CD-ROM == 908.4MB CD-DA
99 minutes == 445,500 sectors == 870.1MB CD-ROM == 999.3MB CD-DA
The International Electrotechnical Commission (IEC) has approved alternate prefixes for binary powers of two. Instead of kilobytes and megabytes we would call them kibibytes and mebibytes, with KiB and MiB replacing KB and MB. This means an 80-minute CD would be rated as holding 703.1MiB or 737.3MB. These haven't yet fallen into common usage. Check the NIST site for full details:

Many CD recording programs will tell you the exact number of 2K sectors available on the CD. This is the only reliable way to know exactly how many sectors are available. 99-minute blanks will actually report incorrect values.

An informal survey conducted by one user found that the deviation between the largest and smallest 74-minute CD-R was about 3500 sectors (47 seconds, or 7MB), which while not inconsequential is nowhere near the difference between 650MB and the 680MB or 700MB figures quoted by some manufacturers. All discs had at least 333,000 sectors, as required by the Red Book specification. has a fairly detailed listing of how much data different brands of media will actually hold. Again, bear in mind that different batches of the same media may have different capacities.

The PCA (Power Calibration Area), PMA (Program Memory Area), TOC (Table of Contents), lead-in, and lead-out areas don't count against the time rating on single-session CDs. You really do get all the storage that the disc is rated for. On standard MODE 1 discs that aren't using packet writing, there is no "formatting overhead". Bear in mind, however, that the "cluster" size is 2K, and that the ISO-9660 filesystem may use more or less space than an MS-DOS FAT or HFS filesystem, so 650MB of files on a hard disk may occupy a different amount of space on a CD.

On a multisession disc, you lose about 23MB of space when the first session is closed (to pave the way for the 2nd session), and about 14MB for each subsequent session. A common mistake when writing multisession CDs is to overestimate the amount of space that will be available for future sessions, so be sure to take this into account.

(If you want the details: the first additional session requires 4500 sectors for the lead-in and 6750 for the lead-out, for a total of 11250 (22.5MB, or 2.5 minutes). Each additional session requires 4500 for the lead-in and 2250 for the lead-out, for a total of 6750 (13.5MB, or 1.5 minutes). You may also need to factor 2-second pre-gaps into the size calculation for each session. On a single-session disc, the overhead for lead-in and lead-out are not counted as part of the user data area, so nothing is "lost" until you go multisession.)

Pressed aluminum CDs are also supposed to hold no more than 74 minutes of audio, but are often tweaked to hold more (see section (3-8)). To convert sectors back to seconds, divide the number of sectors by 75. If your blanks have 333,000 sectors, they have 4440 seconds, which is exactly 74 minutes.

Some packet-writing solutions will take a large bite out of your available disc space. For example, if you use Roxio DirectCD 2.x with CD-RW media, it uses fixed-length packets. This allows random file erase, which means that when you delete a file you actually get the space back, but you're reduced to about 493MB after formatting the disc. More recent versions can get closer to 531MB. See section (4-42) for more info.

Subject: [7-7] Is it okay to write on or stick a label on a disc?

It depends. Use the right kind of pen and you shouldn't have a problem. With labels the situation is a little less certain.

Keep in mind that the data is essentially stored on the top (label side) of the disc. If you damage the top, your data or music is permanently gone. See section (2-1) for a description of the physical makeup of a disc.

Subject: [7-7-1] Can I write on them? What kind of pen should I use?

The ink in some permanent markers can eat away the lacquer coat, which will cause your disc to become unreadable very quickly. Some discs are more vulnerable than other. Unless the disc has some sort of protective top coat (such as a printable surface), always use pens specifically designated as safe for CD-R.

Never write on a disc with a ball-point pen. Pressing down on the label side could pierce or deform the reflective layer.

Examples of pens for CD-Rs include the Dixon Ticonderoga "Redi Sharp Plus", the Sanford "Powermark", and TDK "CD Writer". Some of these are relabeled Staedtler Lumocolor transparency markers (#317-9), which are alcohol-based. Never use a solvent-based "permanent" marker on a CD-R -- it can eat through the lacquer coat and destroy the disc. Memorex sells water-based color "CD Markers" in four-packs (black, blue, red, green).

Many people have had no problems with the popular Sanford "Sharpie" pens, which are alcohol-based. Other people say they've damaged discs by writing on them with a Sharpie, though those discs may have been particularly susceptible. The official word from Sanford is:

"Sanford has used Sharpie Markers on CDs for years and we have never experienced a problem. We do not believe that the Sharpie ink can affect these CDs, however we have not performed any long-term laboratory testing to verify this. We have spoken to many major CD manufacturers about this issue. They use the Sharpie Markers on CDs internally as well, and do not believe that the Sharpie Ink will cause any harm to their products.


Sanford Consumer Affairs"

In any event, the Ultra Fine Sharpie pen looks almost sharp enough to scratch, so sticking with the Fine Point pen is recommended.

So long as you use the right kind of pen, it's okay to write directly on the top surface of the CD, label or no. Use a light touch -- you aren't filling out a form in triplicate. If the prospect makes you nervous, just write in the clear plastic area near the hub.

Subject: [7-7-2] Are labels okay?

The adhesives on some labels can dissolve the protective lacquer coating if the adhesive is based on a solvent that the lacquer is susceptible to. Asymmetric labels can throw the disc out of balance, causing read problems, and labels not designed for CDs might bubble or peel off when subjected to long periods of heat inside a CD drive. Always use labels designed for CD-R media.

There is evidence that labels can shorten CD-R lifetime, so it might be best to label data archives and backups with a pen instead (see section (7-5) for more). Adhesive labels aren't recommended for discs you plan to keep for more than five years.

The best way to feel confident about labeling your discs is to try it yourself. Buy some labels, put them on some discs, leave them someplace warm, and see if they peel off. If they do, you'll need a different kind of media or a different kind of label. Some labels don't adhere very well unless they're attached to a disc with a plain lacquer surface on top, so combining labels with "inkjet printable surface" media may be asking for trouble. One note of caution: this only tells you if the label will peel up right away. It doesn't tell you if the label will still be nice and flat two or three years from now, especially if you live in the tropics where the air is always hot and damp.

Whatever you do, don't try to peel a label off once it's on. You will almost certainly pull part of the recording layer off with the label. If you're going to label a disc, do it immediately, so you can make another copy if the label doesn't adhere smoothly. Any air bubbles in the label that can't be smoothed out immediately are going to cause trouble. Use a label applicator for best results.

It may not be a good idea to put labels on discs that will be fed into a "slot in" CD player, such as those popular in dashboard car CD players. Sometimes the added thickness will cause the disc to get stuck, or the edge will peel up when the motor grabs it.

A number of companies make labels for CDs, and some sell complete kits including applicators and software. Two of the biggest are NEATO, at, and CD Stomper, at The software from includes templates for a variety of different label layouts. Medea International sells labels and labeling software; see Check section (8-3) for other sources.

If you want a label that also covers up the clear plastic part at the center of the disc, search for "hub labels". There are even labels that *only* cover the hub section.

For information about printing directly onto the surface of a disc, see section (7-29).

Some information on CD-R labeling options can be found here:

Sony's web site has a "Downloads & Templates" section with artwork that my prove useful. You can find most CD-related logos on the site (try, scroll down to "Logos" for common formats). Some are also available from

Mike Richter's CD-R primer has a very nice page on labeling discs. See

It is important to keep the CD balanced, or high-speed drives may have trouble reading the disc. According to one report, a disc that had a silk-screened image on the left side of a CD-R (leaving the right half of the disc blank) was unreadable on high-speed drives due to excessive wobbling. Most label kits come with a label-centering device, usually something trivial like a stick that's the same width as the hole in the middle of the CD.

Avery's CD-R labels became quietly unavailable in October 1997. The rumor is that the adhesive caused data corruption problems, so Avery recalled them. There are indications that the adhesive would fail on some discs and start to lift off within a short period of time. If you have Avery labels (#5824) purchased before this date, you should avoid using them. The labels being produced now don't have this problem.

Subject: [7-8] How do CD-Rs behave when microwaved?

Disclaimer: I'm not recommending you put a CD into a microwave. CDs may contain metals that will cause your microwave to arc, destroying the microwave emitter (see cautions about metal objects in the manual for your microwave). Don't try this at home. Better yet, don't try this at all.

The basic process is, take a disc that you don't want anymore, and put it shiny-side-up on something like a coffee mug so it's nowhere near the top, bottom, or sides of the microwave. (Actually, you may want to leave it right-side-up if the disc doesn't have a label, because the foil is closest to the top of the CD.) I'm told it is important to put something in the cup to be on the safe side, so fill it most of the way with water. Try to center it in the microwave. Turn off the lights. Program the microwave for a 5-second burst on "high", and watch the fireworks.

Performing this operation on replicated CDs results in blue sparks that dance along the CD, leaving fractal-ish patterns etched into the reflective aluminum. For those of you not with the program, this also renders the CD unreadable.

Trying this with a green/gold CD-R gives you a similar light show, but the destruction patterns are different. While pressed CDs and CD-RWs don't develop consistent patterns of destruction, CD-Rs tend to form circular patterns, possibly because of the pre-formed spiral groove.

On a different note, CD-Rs seem to smell worse, or at least they start to smell earlier, than pressed CDs. The materials used are non-toxic ("cyanine" comes from the color cyan, not from cyanide), but breathing the fumes is something best avoided.

For the curious, here's a note about why they behave like they do:

"The aluminum layer in a CD-ROM is very thin. The microwave oven induces large currents in the aluminum. This makes enough heat to vaporize the aluminum. You then see a very small lightning storm as electric arcs go through the vaporized aluminum. Within a few seconds there will be many paths etched through the aluminum, leaving behind little metalic islands. Some of the islands will be shaped so that they make very good microwave antennas. These spots will focus the microwave energy, and get very hot. Now you will see just a few bright spots spewing a lot of smoke. The good part of the light show is over, turn off the oven.

I suspect that if you leave the oven going much longer, the CD-ROM will burst into flame. This will smell very bad and may do bad things to your oven and house. Don't do it."
-- Paul Haas (, on

Dreamcast GD-R discs come out just like CD-R, but DVD-R is a whole different experience.

Combining a microwaved CD-R with a tesla coil produces interesting results. See

Subject: [7-9] What can I do with CD-R discs that failed during writing?

If the disc wasn't closed, you can write more data in a new session. If the disc was closed, or was nearly full when the write failed but is still missing important data, then its use as digital media is over.

However, that doesn't mean it's useless. Here are a few ideas:

If you've given up hope of doing something "useful" with it, do something destructive with it. Try to scrape the reflective layer off the top with your fingernail. Drop it on the ground so that it hits edge-on and see if the reflective layer delaminates or the plastic chips. Try to snap it in half. Leave it sitting on a window sill with half the disc covered by a book to see the effects of heat and sunlight. Write on it with nasty permanent markers and see if you can still read it a week later. Apply a CD label then pull it off again. Different brands of media have different levels of tolerance to abuse, and it's useful to understand just how much or how little it takes to destroy a disc.

In one carefully controlled experiment it was determined that CD-Rs behave differently from pressed CDs when you slam them edge-on against the ground. The aluminum ones will chip (once you throw them hard enough, otherwise they just bounce) and create silver confetti. The gold one I tried chipped and the gold layer started peeling, leaving little gold flakes everywhere. One user reported that a Verbatim blue CD developed bubbles even though the plastic was intact. More experimentation is needed (but not around pets, small children, or hard-to-vacuum carpets).

On a different tack, some CD-Rs don't hold up well when immersed in water. Try pouring a little water on a disc, then let it sit until it dries. If the top surface scratches off more easily afterward, you need to be careful around moisture. Silver/blue Verbatim discs seem particularly sensitive.

One comment about snapping discs in half with your fingers: use caution. Depending on the disc and how you break it, you may end up with lots of sharp polycarbonate slivers flying through the air. Wear eye protection, be aware of people around you, and be sure to clean up all the plastic shards afterward.

If you have far more coasters than you want to play with, consider recycling them (section (7-21)).

Subject: [7-10] Where can I find jewel cases and CD sleeves?

There are many vendors. A few are listed below.

You have a lot of choices when it comes to CD packaging. There are single-disc jewel cases, double-sized doubles, single-sized doubles, triples, quads, sextuples, plain colors, neon colors, paper envelopes, Tyvek envelopes, cardboard sleeves, clear jewel cases with black trays, clear jewel cases with built-in trays, CD pockets for use in three-ring binders, and on, and on.

If you can imagine it, it's probably up for sale.

Some URLs to start with:
A warning about some double-disc jewel cases sold by CompUSA can be found at (along with pictures). Apparently the pressure exerted on the hub causes cracks to appear over time. If a disc with a cracked hub is put into a high-speed drive, it may shatter (see section (7-25)).

Subject: [7-11] What's "unbranded" CD-R media?

Simply put, it's a CD-R disc with nothing printed on the top surface. Some people need "plain" discs that they can print on, or simply like them for the aesthetic value. There is no difference in quality or capacity.

Subject: [7-12] How do I repair a scratched CD?

If you scratched the top (label) side of a CD-R, and it no longer works, your disc is toast. (If you scratched it, and it still works, copy the data off while you still can.)

If you scratched the bottom side, then all you've done is etch the polycarbonate (plastic), and it can be repaired like any other CD. A common misconception is that the data is on the bottom, but if you examine it carefully you will see that the data is beneath the label. The laser reads the data through the polycarbonate layer, and if the layer is scratched the laser will refract onto the wrong part of the disc.

For small or radial scratches, the error correction in the CD format will allow the disc to continue working, but if there's too much disruption you will get audible glitches or CD-ROM driver errors.

If the disc works some of the time, you can "repair" it by copying it onto a new CD-R disc. If the disc is always unreadable, or is copy protected, you will need to repair the disc itself.

One product that may be useful is Wipe Out! (, a chemical abrasive that allows you to reduce scratches. Another is Discwasher from

The Repair FAQ at has a section on repairing scratched CDs. Find the "Compact Disc Players and CDROM Drives" section, and skip down to 4.10 and 4.11.

Some people have suggested using plastic polishes or "fine cut" paint polishes sold for removing fine scratches on automobiles. These fill in the scratches and create a more optically consistent surface. Fine metal polishes may also work, and some people claim that plain old white toothpaste does the trick. There is some chance that the filler material will fall out over time, rendering the disc unreadable once again, and possibly gunking up your CD-ROM drive along the way. If you want to fill in the scratches, you should make a copy of the contents to a new disc as soon as possible, and stop using the original.

Subject: [7-13] What's this about a Canadian CD-R tax?

In the United States, a distinction is made between "consumer digital audio" media and data media. You have to pay extra for consumer audio CD-R blanks and DAT tapes, and the music recording industry gets a piece on the assumption that the media will be used to hold commercially recorded material.

Canada has gone a step farther, by placing a levy upon *all* media capable of storing audio. Even the "data" CD-R blanks, which don't work in consumer audio CD-recordable decks, are subject to the levy. Starting Jan 1 2001, the levy was raised from CDN$0.052 to CDN$0.21 (a 4x increase) for CD-R and CD-RW discs.

Some web sites with more information:
See also for a 1999/12/17 announcement that the Levy has gone into effect, and for an announcement about the 2001 price increase. has the 2007 proposal, which continues the CDN$0.21 per disc price. The price for discs purchased in bulk quantities can more than double because of the levy.

Subject: [7-14] Can I get 80mm (3-inch "cd single") CD-Rs?

The 80mm CD didn't catch on everywhere. In some markets, notably the USA, pressed "CD single" discs are rarely seen. The 80mm CD-R made a brief appearance, and then vanished for a while. As of the middle of the year 2000, they were once again easy to find. In mid-2001, Sony started using them in one of their Mavica camera models, and towards the end of 2001 80mm-based MP3 players appeared. They're pretty easy to find now.

Using them is not as straightforward as could be hoped. Most *software* will work just fine, because all CD-Rs have slightly different capacities, especially when you consider 63-minute, 74-minute, and 80-minute blanks. The problems stem from their physical dimensions.

Pretty much all tray-based recorders have grooves for 120mm discs and 80mm discs. However, not all of them can actually record 80mm discs. Web sites for recent drives will sometimes indicate whether or not they're compatible. Some CD recorders can read the discs but not write them, possibly because the clamping mechanism raises the disc to a level where it's no longer sufficiently supported at the edges.

If you have a caddy-based recorder, you will have a problem: while trays have two different rings for 80mm and 120mm discs, caddies don't. According to the Yamaha CDR-102 manual, there is a "Disk Adaptor", referenced as part #ADP08, that sits in the caddy and keeps the disc properly positioned. A device that performed a similar function used to be sold by music stores so that standard players could handle 80mm CD-singles; it looks like a plastic doughnut that clips onto the disc.

If you have one of these, great. If you don't, you may have difficulty finding them. You will likely have even worse luck figuring out how to play an 80mm disc on a "slot in" CD-ROM drive -- the kind where you push the disc into a slot, and it slurps it up. Some manufacturers have indicated that their traction-feed drives work fine with 80mm discs, but before you try it might be wise to have a screwdriver handy.

A less common issue with 80mm discs has to do with playback. A loose sheet included with the CDR-100/102 "CD Expert" manual states:

"An 8-cm disc recorded at normal speed on the CD Expert may not playback correctly on some manufacturer's CD-ROM drives. This is likely on drives that have a playback PLL (phase lock loop) bandwidth of 1.5 kHz. Most drives, however, have a playback PLL bandwidth of 2.5 kHz, in which case this is not a problem."
The final discouragement for 80mm discs is that they only hold 21 minutes of audio (about 95250 sectors on Ritek silver-blue discs, or about 186MB), but at present cost more than their full-sized counterparts. They are an interesting curiosity, and a cute gift when placed in a miniature jewel case, but little more. There appear to be 80mm discs that hold 34 minutes (just shy of 300MB), but these come with the same caveats as 90-minute 120mm discs: the discs have to be constructed at or outside the limits of what the specifications allow, and you may have problems with compatibility.

[ On a personal note: my Plextor 8/20 refuses to accept 80mm discs when I put them in the tray. I was able to use them with a (caddy-load) Yamaha CDR-102 when I put the discs in a CD-single caddy adapter. It turns out that the Plextor 8/20 will write to the discs when the caddy adapter is used for it as well. There seems to be some problem with the Plextor's mechanics when the disc is resting in the 80mm tray. I don't know of a source for the adapters, though I'm told carries them. ]

Subject: [7-15] Where can I find CD-ROM business cards and "shaped" CDs?

You can find CD-ROMs in many interesting shapes, including ovals and rectangles. These are functional CD-ROMs that are, for example, the same size and shape as a traditional business card (well, a really thick business card). They can have your name and contact information printed on the front, and can hold a modest amount of data, typically about 40MB.

Recordable CD-R business cards are available as well.

As with 80mm CDs (see section (7-14)), you may have trouble playing these "discs" on CD-ROM drives that use caddies or have a "slot-in" design.

Some net.vendors (there are many others, but this is a good start):
For information about a 57.5mm disc with 80mm "wings", see

Cutting a CD-R disc into a different shape isn't recommended, because the recording layer tends to delaminate easily once the seal has been broken. Some CD-Rs have appeared in Japan that use a 120mm polycarbonate disc with an 80mm recordable area. This allows the outer polycarbonate to be cut into interesting shapes without affecting the recordable area. Some pictures are available on

What follows are some personal notes on CD-recordable business cards, based on experiments conducted in early 2000. I bought five from for about $3 each. According to CD-R Media Code Identifier, the essential facts are:

Nominal Capacity: 51.219MB (05m 51s 49f / LBA: 26224)
ATIP: 97m 1As 55f
Disc Manufacturer: Lead Data Inc.
Dye: Pthalocyanine (Type 5)
The discs are gold in color, and look like an 80mm disc that was squared off across the top and bottom. They come in clear plastic envelopes that are slightly larger than the discs themselves. Total size is 80mm long and 60mm wide, which is a little off from the standard business card (88mm x 51mm) but not by much.

As with 80mm CD-Rs, my Plextor 8/20 rejected them unless I put them in an 80mm caddy adapter. The adapter doesn't work very well, since it's only holding the disc on two points, but it worked well enough.

I grabbed a local copy of my web page, threw on an autorun.inf and a copy of shellout.exe, and wrote it to the disc with disc-at-once recording. The recorder got upset while writing the leadout, and ECDC (3.5c) reported some fatal errors, but the disc had already been closed enough to be readable in the two CD-ROM drives tried. It's possible that the slight looseness in the caddy adapter caused problems... on future attempts I will try to fasten the disc a little more securely.

The use of these discs as business cards presents some difficulties. If you look at the picture on, you can see that the disc has the same clear hub as a standard disc, which doesn't give you much of a solid background for writing. All is not lost, however: there are other cards with ink-jet printable surfaces, and adhesive business card labels are now available.

Subject: [7-16] Can you tell pressed CDs and silver CD-Rs apart?

The easiest way is to drag something sharp across the top, perhaps some car keys, and watch what happens. If the top surface flakes off easily and seems to want to peel up, it's a CD recordable. If you'd like to be able to use the disc afterward, there are some non-destructive ways too.

In some cases it's easy to tell, e.g. the color is slightly off or there are two different shades of silver. The written areas on a CD-R look slightly different from unwritten areas. A silver CD-R that has been written to capacity is nearly indistinguishable from a pressed disc though, and some pressed discs have distinctly visible regions.

You can get a definitive answer with CD-R Media Code Identifier (6-2-9). Put the disc into a CD recorder and query it. Pressed discs will say "no information". Some CD recorders might have trouble finding the ATIP after the disc has been closed, so do some tests with known discs before jumping to any conclusions.

Subject: [7-17] What's the difference between "data" and "music" blanks?

"Consumer" stand-alone audio CD recorders require special blanks. See section (5-12) for details. There is no difference in quality or composition between "data" blanks and "music" blanks, except for a flag that indicates which one it is. It's likely that "music" blanks are optimized for recording at 1x, since anything you record "live" is by definition recorded at 1x (though some dual-drive systems allow track copying at higher speeds).

You don't have to use "music" blanks to record music on a computer or on a "professional" stand-alone audio CD recorder. Nothing will prevent you from doing so, but there's no advantage to it.

The "music" blanks are more expensive than the "data" blanks because a portion of the price goes to the music industry. The specifics vary from country to country. In the USA, the money goes to the RIAA, which distributes it to artists who have navigated through a complicated application process.

Some manufacturers have on occasion marked low-quality data discs as being "for music", on the assumption that small errors will go unnoticed. Make sure that, if you need the special blanks, you're getting the right thing.

(Technically, there are actually three kinds of blanks: type 1a for CD-ROM or professional audio recording, type 1b for special-purpose applications like PhotoCD, and type 2 for unrestricted use. "Music" blanks are type 2, "data" blanks are type 1a.)

Some disc manufacturers label "music" blanks as "universal use", since they will work on anything.

Subject: [7-18] How do I convert data CD-Rs into "consumer audio" blanks?

The CD-Rs required by "consumer" stand-alone audio recorders ( section (5-12)) are more expensive than the standard "data" CD-Rs. Converting a standard blank into a consumer-audio blank is like converting lead to gold, in two ways: it would save a lot of money, and it's impossible.

CD-Rs have some information pressed into them that cannot be altered. One such tidbit is the Disc Application Flag, which tells the recorder what sort of blank you've inserted.

There are ways to trick certain recorders into accepting other kinds of blanks (some of which are mentioned in section (5-12)), but there is no way to disguise the blank itself.

(For the nit-pickers: apparently some experiments with nuclear reactors and particle accelerators have actually resulted in conversion of lead to gold. It is unlikely that placing a "data" CD-R in a particle accelerator will do anything useful, however.)

Subject: [7-19] Is translucent media bad?

A popular perception is that translucent CD-R media -- discs that are, to some extent, see-through -- are lower in quality than discs you can't see through. The argument is that the discs reflect less light, and as a result are less likely to work in some players.

The argument is without merit. So long as the disc reflects at least 70% of the beam when it strikes a "land", it meets the CD-R specification.

All CD-R media, except for discs treated with an opaque top coating (usually to provide an absorbent surface for ink-jet printers), are to some extent translucent. Take your favorite brand of un-coated disc, write on the top with a black marker, and hold it up to a bright light source. The writing will be visible through the disc, even on widely recommended high-end brands.

Suppose the translucent media had an opaque label added to the top. Now that you can't see through it, is the quality of the media higher?

There is much more to media quality than its ability to reflect the visible light spectrum. It can be argued, of course, that there is a correlation between the process that yields discs that are easy to see through and discs that don't work very well. There is, as yet, no proof that such a correlation exists.

Subject: [7-20] How do I destroy CD-R media beyond all hope of recovery?

This question comes up every once in a while, because somebody with sensitive data wants to obliterate unwanted copies on CD-R. With magnetic media, the problem is well understood, and guidelines have been published for the proper treatment of floppy disks and hard drives. To the best of my knowledge, no such guidelines have been published for CD recordable media.

To be effective and useful, an approach must have two properties: it must guarantee that there is no hope of recovering any data from the media, and it must be safe and easy to implement. The qualifications for the former involve a fair degree of paranoia. If, for example, you want to erase a file from a hard drive while leaving the remaining contents intact, it is necessary to write over every sector in which the file was written several times with different bit patterns. If you just zeroed out the blocks, a sufficiently sensitive device could detect lingering magnetic traces, and possibly reconstruct significant pieces of the original file.

Some possible approaches for CD-R:

Death by physical delamination
Scrape off the reflective layer with something sharp. Can be done by an unskilled worker or simple device. You still need to do something with the reflective layer, though, and there might still be traces of data on the polycarbonate (dye residue).
Death by shredding
Run the disc through an industrial-strength paper shredder. The polycarbonate tends to shatter into many small pieces. The resulting jigsaw puzzle should be exceptionally difficult to reassemble. The trouble is that the reflective layer and underlying dye is very flexible once separated from the polycarbonate, and might not shred well. (A much simpler variant of this is to snap the disc in half. If you do it the right direction, the polycarbonate breaks into several pieces. You may want to tuck the disc inside a magazine or newspaper to control the shrapnel.) Many "home office" shredders will handle CDs now.
Death by drum sander
Secure the disc to a piece of wood, and run it through an industrial drum sander ( These come with dust vacuum hoods, which should minimize the amount of breathable polycarbonate. The system would have to be calibrated carefully though, or the sander might just rip the data layer off and fling it (or, for that matter, fire the whole disc across the room). Using the piece of wood more than once might be problematic, depending on the exact method used to attach discs to it.
Death by chemical delamination
Drop the disc into acetone. That ought to dissolve the top layer and leave little left that's meaningful. Something still needs to be done with the polycarbonate, though, in case it retains any traces of the data, and disposal of acetone can be a problem.
Death by incineration
Pop the disc into a wood-burning stove. Quick, easy, effective, and really bad for the environment. The fumes from burning polycarbonate are not recommended as a treatment for lung disorders. Elevating a CD-R disc above 250C (about 480F) should cause it to become fully "recorded", but it's possible that some traces of the original recording would remain.
Death by microwave
Microwaving a disc for a few seconds renders it pretty well unusable. It's not clear how thorough this process is. A visual inspection suggests that some regions of the disc go relatively untouched.
Death by coherent light
The disc was written by a laser that turned on and off. Presumably it is possible to modify a CD recorder such that it turns the laser on and leaves it on. This would obliterate all of the data on the disc. It's not clear if a sensitive detector could see regions that were "written" twice.
Death by sandblasting
Blasting discs with sand will certainly take the reflective layer off, and do a pretty fair job of scrubbing them clean. The only concern is for whether the delaminated layer gets fully pulverized or just sheared off (and stays intact).
Death by sidewalk
This approach is similar to the others, but can be performed with inexpensive equipment: a patch of rough cement and a rubber-soled shoe. Put the disc, shiny side up, on the sidewalk. Step on it, and twist vigorously while applying pressure. This will gouge the foil and polycarbonate, and with sufficient force may even split the disc itself. More force may be required on disks with adhesive labels, and cleanup can be tricky on a windy day.
There doesn't seem to be a simple answer or perfect method. If you aren't concerned about the NSA or a major national power recovering your data, though, scratching with car keys or snapping in half with your hands should be all the security you need.

Subject: [7-21] Can I recycle old CDs, CD-Rs, and CD-RWs?

Yes. One such recycling company, Polymer Reprocessors (in the UK), has a nice web page describing what happens to the materials. Visit


Subject: [7-22] Is there really a fungus that eats CDs?

Yes. It appears to be limited to tropical climates. Two articles from mid-2001 (no longer on original sites, so links are provided):

The incident in question was discovered by a researcher from Spain who visited Belize in Central America. What is believed to be a strain of Geotrichum entered a CD from the outer edge and destroyed the aluminum reflective layer as well as some of the polycarbonate.

A person in Australia reported a few years earlier that store-bought pressed CDs were getting eaten, but gold CD-Rs were doing rather well.

Subject: [7-23] How do I clean CD-R and CD-RW discs?

The short answer is, clean them the same way you would a pressed CD. Take a lint-free cotton cloth and wipe from the center out. It's important to move in a straight line from the hub to the outside, rather than moving in a circular motion. The act of cleaning could cause the surface to abrade, and the error correction employed is better at correcting scratches and marks that go from the center out.

You have to be a little more careful with CD-Rs than you are with pressed CDs, because the lacquer coating may not resist certain chemicals as well. Some CD-R discs all but fall apart when exposed to alcohol. Some really cheap ones start to dissolve in tap water. Your best bet is to just use a dry, clean, soft, lint-free cloth, like you would use to clean the lens of a camera.

(In practice, a wadded up tissue works pretty well, but it's best to avoid paper products. Lens cleaning papers are great for glass, but polycarbonate is much easier to scratch.)

Subject: [7-24] Are "black" discs different from other discs?

Yes and no. Your eyes can tell you that the disc is different, but the laser in the CD player can't.

A "black" disc, popularized by the tint added to Playstation games, has had color added to the polycarbonate layer. The tint looks very dark to the eye, but so long as it doesn't absorb or disperse too much light in the laser wavelength it won't interfere with disc performance. If you hold the disc in front of a light, you may discover that your "black" disc is actually very dark red.

Some people have suggested that, by blocking other light, the coloration enhances the performance of the disc. This makes about as much sense as drawing around the outside of the disc with a green magic marker (a popular myth from the 1980s).

If you find that "black" discs work poorly or especially well, you haven't discovered anything different from what most owners of CD recorders know: some discs just work better than others. The tint in the plastic isn't likely to be involved.

(Some users have done some fairly careful testing, and found that "black" audio discs sounded better than non-black discs from the same manufacturer. I haven't seen a controlled double-blind study that reached this conclusion, but there is anecdotal evidence to suggest that the colored polycarbonate causes the discs to sound different.)

Subject: [7-25] My disc just shattered in the CD drive!

This is rare but not unheard-of. Spinning an object at high speed puts it under a lot of strain. Poorly-balanced discs can cause vibrations and make the problem worse.

Drives rated at 52x typically spin somewhere between 10,000 and 12,000 RPM (see section (5-22) to see how this is calculated). This is not enough to shatter a disc in good condition, but more than enough to destroy a disc with minor defects. This is one reason why Sony's 52x drives default to 40x maximum, with a "turbo boost" feature that enables 52x reading and writing.

Super-fast drives, e.g. 72x, are actually spinning more slowly, but employ multiple read lasers to read from more than one area of the disc at a time. has some warnings and safety advice. There is a PDF document containing a thorough analysis of the problem. The study concluded that uncracked discs are not expected to shatter in 40x and 52x drives, but discs with small cracks near the hub of the disc are at risk.

If you have a disc with a visible crack in it, DO NOT use it in your CD-ROM drive unless you can reduce the speed to 8x or below (the slower the better). Not all drives can be slowed. For Plextor models use the tools that came with the drive; for some models there are speed-reduction applications available on the web; for others you're simply out of luck. Nero DriveSpeed ( will work for many drives.

Some web pages with destructive experiments:

An episode of the Discovery Channel's "Mythbusters" TV show demonstrated discs flying apart near 30,000 RPM. This speed would only be necessary for a 150x drive. Apparently they assumed that 52x drives read at 52x across the entire disc, rather than just at the outside where the amount of data read per revolution is higher.

Subject: [7-26] How do I tell which side on a silver/silver disc is up?

There is one approach guaranteed to work: put the disc in the drive. If it works, you have it right. If it doesn't, eject it and turn it over.

Alternate approach: many discs have numbers or letters printed near the hub. If they appear to be written backwards, the disc is upside-down.

Another approach: hold the disc edge-on in front of you, so you're looking right across the surface of the disc. Tilt it up slightly, and look closely at the edge farthest from you. When it's the right way up you'll just see the label, when it's the wrong way up you'll be able to see some light through the polycarbonate.

Yet another approach: the area of the disc near the hub may feel different (one side may have a groove or a lump that the other doesn't). Figure out which side is which, then remember how the disc feels.

Subject: [7-27] How should I handle and store CDs?

This list comes substantially from NIST Special Publication 500-252, available from Most of it is common sense.

A temperature between 20C (68F) and 4C (39F) with a relative humidity of 20-50% is recommended. Before you go stuffing all of your discs in the refrigerator, make note of the fact that rapid changes in temperature and humidity can be harmful. You would need to let your discs slowly come up to room temperature before placing them in a CD player. Discs that are accessed frequently should be stored in an environment similar to the one in which they will be played.

Because the data layer on recordable DVDs is sandwiched inside the disc, rather than sitting on top, they may hold up better over time.

Subject: [7-28] What causes the rainbow effect when looking at the data side?

A CD has a single spiral track, each revolution of which is separated by 1.6 microns on a 74-minute disc (less on higher-capacity discs). The mirrored "grooves" act as a reflection diffraction grating, causing interference patterns in the reflected light.

Some related web sites:

Subject: [7-29] Can I print directly on a CD-R?

Yes, with the right setup. You have to use media with a printable surface that holds ink, and you need a disc printer. One equipment source is Primera Technology (

It's also possible to use offset printing (the process used to print newspapers and magazines). Some additional information can be found at

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