by cfitz on Thu Nov 28, 2002 3:19 am
BuddhaTB has given you good advice. But, if you want to explore more, here are some starting points:
1. lacquer: It is important for this to be tough, since it protects the most vulnerable top (yes, top) side of the CD. You won't find much information about this, but some manufacturers such as Mitsui claim special "heavy-duty" lacquers (they call theirs "Diamond Coat" - it does look thicker and tougher than others).
2. reflective layer: The two choices are silver or gold. The silver in pressed CD's is actually aluminum (Al), but in CD-R's it is a true silver (Ag) alloy. The gold should be actual gold (Au), but some manufacturers have been known to add color to their discs to make silver look like gold. The silver has higher reflectance in the infrared band of CD lasers so it returns slightly more power to the laser, but it can oxidize if exposed to the air. Gold is chemically nonreacitve (it is a noble element) so it will always remain shiny. In a well-made CD no oxygen will get to the reflective layer, so this shouldn't be an issue. However I have a bad batch of Sony CD-Rs that I bought ~9 months ago that have started corroding from the edges. Some long-term archivests swear by gold for the extra insurance. These days I think Mitsui is your best source for genuine gold CDs - beware of CDs that are colored gold but aren't actually gold.
3. dye: The three main families are cyanine (the original dye-type, developed by Taiyo Yuden as the reference media when the CD-R standard was being drawn up), phthalocyanine and AZO.
Cyanine is easiest to burn, since it has the most tolerance to variations in laser power. However, cyanine in its native state is sensitive to light so it must be stabilized with added chemicals. Projected lifetimes in a protected environment are 30 to 70 years. Color is blue-green.
Phthalocyanine was the second family to be developed. It is less tolerant of variations in laser power so requires better control to burn properly. It is not sensitive to light in its native state, so is naturally more resistant to degradation due to exposure to light. Claimed lifetimes have ranged as high as 200 years. Color is a very light gold with a hint of green.
AZO is unique to Mitsubishi Chemical/Verbatim. It comes in two variants. The original metal AZO is very dark blue but only good for lower burning speeds, up to about 16x maximum. Super AZO is a variant designed for higher speed burning. It is a lighter shade of blue. Both are claimed to have lifetimes exceeding 100 years.
4. substrate: As far as I know, all CD's are made wih a polycarbonate substrate. Polycarbonate is a very tough, impact resistant plastic. I think the only difference you will see here is that some cheap manufacturers may use a thinner substrate than quality brands.
By the way, your diagram is in error. The layers should be (as seen top to bottom while sitting in your burner, where "top" is the label side of the disc):
label
lacquer
reflective layer
dye
substrate
/\
/\
laser
I hope this gives you a little information. Search the web for more.
cfitz