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Archival Gold with Scratch-Armor

Non-technical Version                                                                                              By Steve Lehman, Microsoft Engineer (MCSE)

This is written in plain, non-technical language for easy reading.  Better than a highly technical white paper.  
An interesting read, this article tells the difference between regular computer discs and Archival Gold discs.  
There are two basic materials that make both discs.  This can help you understand them better   

Dimensions for a Standard Compact Disc (CD)
A standard CD is 1.2 mm (0.047 inch) thick, about 110 mm (4.7 inch) or 80 mm (3.150 inches) in diameter, made from
polycarbonate. They have a storage capacity of 74 minutes of audio or 650 Megabytes of data, leaving enough space for
encoding.  Similarly, CD-RW have almost the same capacity, but with 80 minutes of audio and up to 700 Megabytes.  

Disc Manufacturing
At manufacturing, CDs are not “empty” as they are made with a spiral grove called the “pregroove” which helps the laser
stay on track consistently.  The pregroove also contains information about the CD manufacturer, the dye used, media
information and disc length. The pregroove is never replaced by data.  It comes to the manufacture this way and is
used by the manufacturer for its technical attributes.  Each disc is numbers and the disc number is a hidden attribute
within a computer.  Only once did this information show to the public when Sony once manufactured a disc drive which
showed disc numbers mistakenly but only seen in Windows Explorer.  Those discs were replaced shortly after.  

Two Different Types of Discs
There are two types of dye on dis on the reflector side of a disc, the side where they are recorded with data.  The first kind of
dye is cyanine (green) dye on the cheaper store-bought CD’s, ones you buy at a store in large quantities.  

Cheap-priced store-bought discs (green dye)
Made with cyanine dye, which produces the green dye on its reflective side, these are chemically unstable and therefore
unsuitable for archival usage, as they fade and become unreadable in very few years. A CD recorder writes data to a CD by
a laser with medium to intensive heat to the organic dye. This process does not produce pits, instead, the heat permanently
changes the optical properties of the dye. The changes or intensity of the reflected laser radiation is transformed into
electrical signals from which digital information is decoded.  

Archival Gold Dye Discs
Another type of CD has a gold dye, which does not use its reflective layer in the same exact way but does use it somewhat.
The dye is really a protective shield for the data which is recorded above or inside its gold layer.  Inside the layer the same
type of recording takes place as the green dye discs but its more protected.  These are quite a bit more expensive, more
reliable, and is made from phthalocyanine dye, which produces its gold color.  Again, data is recorded above this gold layer.  
The very few manufacturers who produce them use 24 carat gold for this layer. The gold layer produces longevity and
scratch protection. Phthalocyanine is a stable dye, which does not need stabilizers, unlike the cheaper discs which
are really a "hit or miss" if you will get a disc that is stable enough to use for data but its cheap enough to toss away.  

CD’s based on this are often given a lifetime span of 100 years for its DVD and 300 years for CD without reasoning.
Unlike cyanine, phthalocyanine (gold) dye is less resistant to UV rays and CD-R’s made from this type of dye can show
weakness after only two weeks if left in direct sunlight. Left inside of a hot car can greatly degrade the disc, best kept
indoors.  Those who buy this type of media know to keep it away from UV light, up until now, they were sold to photo
professionals. This type of dye must use a hotter laser such as Light Scribe among more manufacturer's who make a hot
laser. Hotter lasers are more accurately adjusted for its data-writes.

Gold discs, although more expensive, is made by only a few manufacturers.  Few dealers sell them locally. Phthalocyanine
or gold CD do not suffer from the same problems as the cyanine green-dye CD. Manufactures of gold based CD boast 24
carat gold layers. These manufacturers estimate their CD longevity to be as high as 300 years and 100 years for DVD.

Types of Recordings
A disc can be “burned” by using several methods. First, the Disc-At-Once recording method is used for audio tracks or
music and then is closed for read-only operation on music players. It is
not generally used to record data. The Track-At-
, method can record audio as well as data, and it can be left open for more data to be added later.  Packet Writing is
mostly used on CD-RW’s allowing data to be written onto the same tracks with repeated use.  This is the same packet
writing used in memory and data streams through a computer as data packets are sized in 32 bits packets and 64 bit
packets.  The large can move data quicker for its size and volume of data being moved.    

Not a Real McCoy
Some ordinary store-bought CD are colored gold but not the same archival-quality gold CD.  It does have a cyanine (green)
layer on the CD. Be careful to look close, as those manufacturers simply add gold color to disguise their lesser stable
cyanine made CD.  They degrade as quickly as a regular cyanine CD.  According to research conducted by J. Perdereau,
their longevity is expected to be 10 years or lesser.   (see “lifespan” at http:
//en.wikipedia.org/wiki/CD-R ).

CD Labeling:
It is recommended if using adhesive CD labels that the labels be specifically made for CD’s. An unbalanced CD can vibrate
inside a recorder causing read and write errors and damage to the recorder. Off-balance CD can run a muck inside the
machine and until it ejects, you cannot do anything about it. Using a permanent marking pen is common practice but
solvents from such pens can affect the dye layer. It is recommended to use non-solvent marking pens.

Disposing CD-R’s is not so easy. CD’s present a possible security risk if it contains private data. They cannot be erased
permanently with a massive re-write since a track is closed, especially after adding more data to the tracks. Paper
shredders are designed with a slot for shredding discs.  Look into it.