GETTING MORE TALE #515: Dye, Dye My Darling
Have you ever wondered how a CD-R burner works?
It’s quite complicated actually, but the basic idea is that data is encoded in binary “pits” and “land”. If you recall your grade 10 math, binary allows you to record any data in ones and zeros. In the CD world, this translates to “pits” and “land”. Think of the pits as zeros, and the land as ones. When you burn a CD at home, musical data is encoded with a laser. The laser doesn’t actually etch the plastic or metal layers of a disc. Instead, it burns the data into a layer of dye. It is this dye that gives a blank CD its typical colours. Once this information is properly encoded onto the blank CD, you can then play it on most household disc players. But they don’t last forever. The colour of the disc can be a clue how much life it has. It can help indicate what dye was used in manufacturing.
- Cyanine dye (green)
These are the earliest blanks made, with a layer of dye that was also UV sensitive. Unfortunately this meant that your CD could be destroyed by exposing it to direct sunlight. The dyes were improved to make them more stable, but many people had their data destroyed simply by leaving the disc out, playing side up, where sunlight could get to it.
- Phthalocyanine (gold, silver, light green)
A more stable form of dye. You’d have to leave your CD out in sunlight for two weeks to destroy it. Unfortunately phthalocyanine dyes are more sensitive to the writing laser, and these discs required some technical advances to make for a good recording.
- Azo (dark blue)
Rated for a storage lifetime of decades. More stable than the other two dyes. It would take a month of sunlight to destroy an azo-based disc. Also capable of faster writing speeds than other dyes.
Because it would have been easy to look at a green CD and say, “Nope, I’m not buying this one,” disc manufacturers tricked you by adding other colours to the dyes. But the type of dye is only one factor in how good your CD sounds and how long it lasts. A CD is like a sandwich made of plastic with layers in between where the data is stored. Poorly manufactured CD-Rs allow moisture to seep in between the layers and destroy the disc. And of course the quality of the burner is also critical to a good sounding CD-R. And be careful if you’re labelling your disc with a marker. Sometimes solvents from markers can react with the dyes.
In very rare cases, CDs and even DVDs have been known to explode during burning, according to a New York Times article from 2004. It happened when a disc was spun too quickly, probably as a result of heat from the burning laser combined with centrifugal force. This is why the upper limit for burning a CD is 56x. Go faster than that and your music could go BOOM (and not in a good way).
A re-writable CD is different still from a dye-based CD-R. A CD-RW (which can be re-written thousands of times) uses a metal alloy layer that is physically liquefied by the laser. It’s crystalline before burning, but less reflective after burning. Therefore a CD-RW has pits and lands made of more and less reflective spots on the disc. And if you don’t like it, you can start all over again. The laser re-heats the alloy, restoring it to its crystalline reflective state.
It’s all very technical and interesting, but how often do you record a CD today? Though burning a CD will always be a pastime for many music fans, the majority have happily moved on to easier and quicker flash storage. Is that as fascinating as a laser etching your music onto a disc? No, but however you handle your music collection is up to you.