CD Rom colours???

[Hermia]

I'm probably not going to explain this very well, but you know how some CDs/CD roms are different colours on the underside (usually silver, blue or gold). What do these colours mean, do they indicate the type/quality of the disc?

[Sequin]

They indicate the type of laser sensitive dye used in the manufacture - different manufacturers use different dyes

[Mobius1]

Actually it's an indicator as to what material has been used in the disc's manufacture

CD-ROMs and DVD-ROMs use a thin metallic layer, usually aluminium, beneath the polycarbonate plastic substrate (the hard surface). Laser sensitive dye is not used in general manufacture of ROM discs. These tend to be gold or silver in colour but other semi transparent plastic substrate colours can be used, such as the black used in old PlayStation games and purple used in original PlayStation 2 game discs).

Laser sensitive dye or "organic polymer dye" is used in consumer recordable disc media i.e. CD-R and DVD-R. This is usually a blue/green colour, but again, manufacturers can make different colours for the dye.

Rewritable media, i.e. CD-RW and DVD-RW types use an optical phase change layer, rather than dye, which allows them to be re-written. In most consumer rewritable media I've come accross, this is most commonly a silver/grey colour, and I've not seen any other colours available (as they may affect the read quality over time as the disc degrades).

So, in some cases they can indicate the type of the disc, but only to a limited degree. The best way to know what type of disc you're looking at is, is to look at the logo on it's non-read surface.

[Hermia]

Thanks for your answer. The reason I'm asking this is 'cause I work in a library and we are having huge problems with some of the CD audio books we buy. They disintegrate within months and they are all blue coloured. I was trying to work out whether the company is using an inferior CDrom or whether something else is to blame.

[Mobius1]

It certainly sounds like CD-R media then.

I've had instances myself where CD-R disc quality (or at least the readability of the data on the disc itself) degrades very quickly. Can't really say why, as it seems to occur arbitrarily after extended use of the disc, whereby it won't read in some players anymore or stutters. To be honest I don't even know if it's to do with the quality or brand of the recordable disc, as I've had the problem happen with TDK and Memorex brand discs.

It might be worth calling up the supplies and enquiring about the problem though. Supplying discs that wear out that quickly really isn't on.