We all know what a CD is, we use it to play music in our cars and home stereos. By definition it is an optical disc used to store digital data, usually 80 or 120mm in diameter. It was introduced in 1982 and is now the standard playback format for commercial audio recordings. An audio CD consists of one or more stereo tracks of audio, stored using the 16 bit PCM (Pulse code modulation), with a sampling rate of 44.1 kHz. Originally the first audio CD was going to hold 1 hour of audio, with a disc diameter of 11 ½ cm. The final length of the CD was bumped up to 74 minutes. Some say that this was because Sony’s vice-president suggested it, so that it would be able to fit the full recording of Beethoven’s 9th symphony. But this is most likely untrue, although it sounds pretty cool! In 1988 the CD-R (also known as the CD-WO (CD Write Once)) was introduced. It retained all the functionality of the CD, plus it added the feature of being able to store both music and data. Let’s take a deeper look into the world of the CD-R disc.

The standard CD-R disc is also an 80 or 120mm disc made of polycarbonate, with a 74 minute or 650MB storage capacity. There are also non-standard CD-R discs that hole a variety of times and amounts of information. The most widely used disc is the 80 minute type. The polycarbonate disc contains a spiral groove printed in an organic dye, which guides the laser when reading and writing the disc. On top of that organic dye is a thin layer of silver or gold, which is then topped with a protective layer of photo-polymerizable lacquer. There are 3 different dye formulas used in CD-Rs. They are:

1. Cynanine dyes - These dyes are mostly green in color, and for the most part are unstable. This instability makes this dye unsuitable for archival purposes, since the dye will fade and become unreadable after a period of time.

2. Azo dye - This dye is usually blue in color, and is stable, so it is typically rated with a lifetime in the area of decades.

3. Phthalocyanine dye - These dyes can be silver, gold, or light green. They are similar with Azo dyes, and are usually rated with a lifetime in the area of hundreds of years.

There are a couple different write methods used in CD-Rs, you may be familiar with them if you have burned CD-Rs on your home computer. They are:

1. Disc at once – This method leaves no gaps between tracks and is “closed”, meaning that no more data can be added at any later dates. This works well for live performances.

2. Track at once – This method places gaps between each track and allows for data to be written to the disc at a later date. This method also allows for audio and data to reside on the same disc.

Because CD-R media will degrade over time, there are a few things you must keep in mind in order to maximize the life expectancy of your CD-R. This is not a full list, but these are definitely important issues one should pay attention to when handling CD-Rs.

1. Handle disc edges only – This will help you to avoid bending the disc as well as help keep fingerprints off of the disc.

2. CD-R discs must be stored in a cool, dry place. The optimal storage temperature for your CD-R is 41-68 degrees Fahrenheit.

3. If you are going to write on your disc, use a felt tip water based marker. Alcohol based markers are second best, but not recommended. Xylene and toluene based markers should never be used.