In the context of the interest I have in evaluating the reliability of optical discs (more specifically CD-R and DVD-R whose use for archival purposes fully justify special attention), I found an interesting document published by the Electronic Library team of the French National Library (BNF).
The BNF is the recipient of the legal deposit in France and, in this context, archives all the Audio-CD (CD-DA) phonographic production since 1983. Alain Carou and Thi Phuong Nguyen summarized the observations made in this context, with two decennies of history. Overall, the resulting opinion is quite re-assuring since the CD-DA comply with their specification and promises (the most conservative estimations gave 20 years of shelf life for pressed optical CDs).
Furthermore, the published report (titled ” Contribution Ã l’Ã©tude du vieillissement des CD – Recherches sur les collections de la BibliothÃ¨que nationale
de France ” – French for Contribution to the studies about CD ageing – Research about the collections at the French National Library) finally contains many interesting observations and informations inside its 21 pages. In order to entice you, here are some of the elements I noticed:
- A clear explanation about the measurable parameters of CD quality (BLER, BERL, C1/C2, jitter, etc.), in French.
- Detailled comments about the problems coming from silver+nitrocellulosic varnish discs (PDO UK discs known as “bronzed” or Optimes dics), where the varnish did not play its normal protecting role and let the silver layer corrode quickly (more quickly than in the case of aluminium layers).
- An analysis of “misted” discs where the polycarbonate substrate degraded much quicker than expected (bad chemical stabilization?).
A must read.