What kinds of media are there?

The basic building blocks of CD-R media are cyanine dye, which is cyan blue in color, and phthalocyanine dye, which is more or less colorless. The reflective layer is either a silvery alloy, the exact composition of which is proprietary, or 24K gold.

There are gold/gold, green/gold, silver/blue, and silver/silver CD-Rs. The apparent color is determined by the color of the reflective layer (gold or silver) and the color of the dye (cyan or colorless). For example, green/gold discs combine a gold reflective layer with a cyan-colored dye, resulting in a gold appearance on the label side and a green appearance on the writing side.

Many people have jumped to the conclusion that "silver" discs are made of silver, and have attempted to speculate on the relative reflectivity and lifespan of the media based on that assumption. Until an industry representative issues a statement concerning the actual composition, it would be unwise to assume that the reflective layer has any specific formulation.

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. 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.

The reason why there are multiple formulations is that the materials and process 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 "Info guard") 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.

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 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.

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

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.

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 OEMed from one of the major 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.

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.

It may be a good idea to start by selecting media that is certified for your recorder's desired write speed. This is particularly important for CD-RW discs, which won't be written faster than the disc is rated for, regardless of the top speed of the drive. Using 8x-certified CD-R media when recording at 8x isn't a bad idea, but doesn't seem to be essential.

The Orange Book standard was written based on the original "green" discs from Taiyo Yuden. "Green" media is more forgiving of marginal read/write power variations than "gold", making them easier to read on some drives. TDK's media has been a popular choice for some time.

"Gold" media manufacturers claim it has a longer lifespan and will work better in higher speed recording than "green" discs. Mitsui's gold/gold discs are recommended by some vendors, and in some informal and unscientific tests were more compatible with car CD players than Kodak gold or TDK green discs. The response to Mitsui's "platinum" media has also been favorable. Different test labs will tell you different things.

There is no advantage to using expensive "audio CD-Rs". 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.

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

I personally like Memorex. Very good for the money.

How long do CD-Rs and CD-RWs last?

There doesn't seem to be a clear answer for CD-RW. 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.

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.

How much data can they hold? 650MB? 680MB?

There are 21-minute (80mm/3-inch), 63-minute, 74-minute, and 80-minute CD-Rs. These translate into data storage capacities of 184MB, 553MB, 650MB, and 700MB respectively (note these numbers are approximate).

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 CD-R and RAM manufacturers do. The "MB" for CD-Rs and RAM means 1024x1024, but for hard drives it means 1000x1000. Keep this in mind when purchasing a hard drive that needs to hold an entire CD. 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.)

Spelled out simply:

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

The PCA (Program Calibration Area), PMA (Program Memory Area), TOC (Table of Contents), lead-in, and lead-out areas don't count against the 74-minute 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, 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.

Pressed aluminum CDs are also supposed to hold no more than 74 minutes of audio, but are often tweaked to hold more . This can make life interesting when attempting to copy CDs. BTW, to convert blocks to seconds, divide the number of blocks by 75. If your blanks have 333,000 blocks, 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 Adaptec 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. (You can create a CD-RW with variable-length packets by formatting a CD-R with DirectCD and then doing an image copy from CD-R to CD-RW. You regain the space but lose the ability to do random file erase.)

Is it okay to write on or stick a label on a disc?

Only if you're careful. 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. Similarly, the ink in some kinds of pens may damage the top coating of the disc

There are pens recommended specifically for writing on CD-Rs. Examples include the Dixon Ticonderoga "Redi Sharp Plus", the Sanford "Powermark", TDK "CD Writer", and Smart and Friendly "CD Speed Marker". Some of these are relabeled Staedtler Lumocolor transparency markers, which are water-based. Never use a solvent-based pen on a CD-R.

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. In any event, the Ultra Fine 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. If the prospect makes you nervous, just write in the clear plastic area near the hub, or only use discs with a printable top surface.

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.

Only use labels made specifically for recordable CDs .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.

Where can I find jewel cases and CD sleeves?

There are many vendors.

Incidentally, 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.

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.

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.

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 alone 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.

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