Silver and gold
The reflective and dye layers are the most important layers in the equation. The reflective layer can be gold, silver, or a combination of both. Gold is generally thought of as the most stable in the long run since it's the least reactive with dyes and, therefore, less prone to corrosion. However, there's also a good argument for silver, which was specified in the original standard because it's more reflective and, therefore, more easily read by players. Manufacturers also claim that dye formulas have been improved to the point where reactions with the reflective layer are no longer an issue.

Fool's gold
Buying a disc with real gold in it can be a challenge because you can't go simply on product labeling or even the color of the disc. The packaging on some generic discs may use the word gold strictly as an advertising ploy. And disc colors can be deceptive. The upper layer can be any color of the rainbow, and manufacturers have also recently taken to coloring the transparent bottom layer. Some discs, for instance, have a gold-colored upper protective layer, yet they actually use a silver reflective layer.

How can you tell fool's gold from the real thing? If store personnel cannot confirm the truth for you, ask them if you can open a package and look at the disc. If you look very closely at the bottom layer, even through a color, you should be able to see a warm glow to the disc that signals true gold inside. Comparing a gold disc to a silver disc makes it easier to see the difference. If you cannot perform any of these checks, your best bet is to research company Web sites for the specification, or you can just learn from experience by buying different brands and comparing them.

To dye for
The photoreactive-dye layer comes in more variations than the reflective layer does. The original official CD standard called for TDK's Azo dye, which is dark blue. However, a number of other dyes, such as the lighter blue cyanine, have been developed and employed since--basically so that vendors don't have to pay each other royalties. Some dyes, such as phthalocyanine, are lighter than others and don't produce as distinct a variation in color between burn marks and the unburned areas. This has been the traditional knock on common reflective/dye combinations such as gold/phthalocyanine. By and large, however, CD-ROM-drive manufacturers have learned to compensate for the differences in dyes. According to Katherine Cochrane, "Some recorders (like my first one) do have more trouble recording on phthalocyanine, but the discs do have a reputation for lasting longer than cyanine ones."

If this explanation leaves you seeing more colors than those on a psychedelic poster, try not to worry. Unless you're having real problems with discs that can't be read in other drives, the dye/metal controversy will probably not affect you much.

That said, we recommend discs with a gold reflective layer for archiving because under adverse conditions, the more stable nature of gold could be the difference between retaining your data and suffering corrosive heartbreak. But for the best compatibility with the widest variety of drives and players, use discs with a silver reflective layer--their higher reflectivity may make them more readable in older players with weak lasers.