Storing CDR and DVD-R's

[KRSESQ]

My cheap Neato cd labeller does a great job of centering labels. Never noticed any abnormal vibration when they're spinning. No idea, however, how long the labels will stay on (using Neato brand labels exclusively).

Kevin

[William]

Originally posted by az
How about special CDR pens?

Asymmetric labels can kill your CD drive, so you shouldn't use them anyway

AZ

Yes, asymetric labels are bad. Although drives can be killed by "perfect" MS CDs shattering in them (OK, so it's only happened once, but it was my combo drive that it wrote off ).

But as for special CDR pens, they generally use water as the solvent rather than anything nastier. Howevver, the ink still has a bad effect. If you really must label the CD, then the little clear section of the hub should be OK, at least according to current thinking (read no one has done accelerated ageing testing that yet).

[KuroNeko]

Labels(i.e. the glue)/ink are not always bad, but since they'll sell anything as "for CDR", better not use it.

Pens "for CDR" are OK, if they actually _are_ for CDR. Just don't believe anything they promise...

Ideal: discs with _real_ gold as reflective layer (gold-silver mix is second choice, aluminum comes last). Gold never oxidizes. Even if ink damages the laquer - it can't hurt much. Silver can, in very extreme circumstances. Aluminum will oxidize _fast_ whenever and wherever exposed to air.

Neko

[William]

True, but a) most CDs use silver reflective layers now. I don't think that any write once media was actualy using an aluminium layer in production yet (but they want to, to cut maufacturing costs).
b) Do you really want to be using a disc that has started falling apart?

[KuroNeko]

a. think again. Most CDR use aluminum now. Don't be fooled by terms like "silverspeed" and the likes. Just because they use terms like silver and gold in the name, doesn't mean they actually use real gold and silver. They just refer to the color the discs look like.

b. just because the spot where you wrote has a thinner laquer doesn't mean the disc will "fall apart". I would avoid glue-on labels though. Printing on discs is OK if you use dics especially made for this - they have a special layer, and with suitable brand inks. Cheap refill cartridges are not a good idea. Pens shouldn't be a problem in most cases.

Neko

[wkulecz]

I've been flamed for saying this before, but no optical media other than pigment ink on acid-free paper has demonstrated longer data retension than has magnetic media in the real world.

I recently pulled some files off an ~15 year old 5-1/2 inch floppy disk without problems (other than finding the drive to read it in! good thing I'm such a pack rat).

Back up your important stuff on removable hard drives. Forget about CD/DVD R/RW/RAM except for working copies. For anything really important you need at least one offsite backup. Optical is fine for "incremental" backup as even the cheapest CD-R work fine for a couple of months.

--wally.

[Brian Ellis]

Wally

Sorry, I would never rely on magnetic media for long term archiving of valuable material. Tapes stretch, shrink, print-through, lose their coating and do all sorts of 'orrible things, even when well-stored. I used to have all my company data was originally backed up on QIC tapes and, on the few occasions when we tried to retrieve them, it was really touch and go whether we could. Floppies are better but certainly could never be relied upon (I've had at least a couple of dozen fail on me and how many wouldn't even format?). I've never had one single CD-R fail after it had been checked after recording and we used this method exclusively in my company from about 1994 through to its liquidation in 2000 (we destroyed over 200 CD-Rs at the end, the legal requirements for archiving essential info for 10 years being in 30 files of hard copy - not backed up). I would not rely on hard discs, either: had too many fail on me at crucial moments (usually just before backing them up!). I do agree that ink on paper or, better, parchment stands the test of time but is not very flame-retardant. Actually, black laser/photocopy on interleaved alum/halogen-free paper (special archiving quality) has an estimated minimum lifetime under archive conditions (20-25°C, 40-50% RH, chemically filtered air) of over 250 years. However, archival interleaving is essential, to prevent ink transfer.

[az]

The problem with gold is that its reflectivity is quite low, so you may have problems reading golden DCRs.

AZ

[Brian Ellis]

Sorry, AZ, off the mark!! The spectral reflectivity of gold, at the laser wavelengths is excellent, actually marginally better than aluminium and much better than silver.

[az]

Why is it then that my HiFi CD player can only play the silverest of blue CDRs and my old Pioneer 12x CD ROM drive had problems with those golden CDRs that were normal in '98, but not any at all with newer silver blue CDRs?

AZ

[Brian Ellis]

Nothing to do with the metallisation, but with the dye layer, AZ.

[az]

but doesn't the dye layer affect reflectivity, too? And wouldn't then the reflective layer only be one part of the equation?

I don't want to be a smartass, I just try to understand it

AZ

[William]

Reflectivity of a thick gold layer is about 94% in the infrared part of the optical spectrum. Attenuation in the dye layer decreases the intensity of the return laser beam to about 75% of the incident beam. Thinner gold layers may reduce this to values near the 65% minimum allowed by standards. Silver is less expensive than gold, and has equal or better optical properties.

Silver has an infrared reflectance of about 96% that is higher than that of gold. After absorption by the dye layer, the intensity of the return beam is about 77% of that of the incident beam, very near that of a CD-ROM disc. At present, the thickness of the silver layer is not a significant cost factor, although this may change in the future. Thick silver may actually be superior to thin gold because of its constant reflectivity. Small variations in thickness of a thick coating have minimal effect on the reflectance, while the same variations significantly modify the optical properties of a thin coating.

All metal layers have thickness variations, but reflectance from thick layers is not affected because the penetration depth of light is only a fraction of the thickness. Thin layers also have thickness variations, but these are now comparable to penetration depth and significantly modify reflectivity. This results in variations in the intensity of the returned laser beam during rotation of the disc. Such variations have been found to affect the quality of audio discs, and may also influence data quality.

from media sciences.

[Dr Mordrid]

Reflectivity of the silver/gold layer is only part of the story.

Dye also matters, and this is where the evolution of DVD decks comes into play. In the early DVD decks there was only one laser and it had a 640 nm wavelength. Unfortunately CD readers use a different wavelength: 780 nm.

The dyes in CD-R's have a very narrow band of wavelengths at which they efficiently reflect. At the 780 nm wavelenth used in CD readers they reflect about 65% of the laser beam, but at the 640 nm wavelenth used by DVD readers they only reflect 10%.

Not good....

Back in ~1995 an attempt to create a CD Type II disk that could be read at both wavelengths was begun, but it failed after a couple of years because it was too costly.

After that dual laser pickups came along. These had both a 640 nm and a 780 nm laser in one pickup, but it was some time before they were universally adopted and even then some worked a lot better than others. As a result many pre-dual pickup and early-dual DVD decks just don't work well at all with CD-R. Later on improved pickups used a single lens, along with other advances, and CD-R compatability improved across the board.

Further compatability improvements for VCD came along with improved DVD deck chipsets by several makers. Later on people started pressing for SVCD support, but this had to wait for standards organizations to pick which SVCD standard would be accepted: C-Cubes or the Chinese ChaoJi standard. ChaoJi won out.

Now...sometimes the same decks that had problems with CD-R will work fine with CD-RW. The main reason is that many CD-RW's are silvery and very often more transparent than the blue/green CD-R's. This ups the signal level enough for the pickup to be able to read the disk.

Dr. Mordrid

[William]

An erasable is quite different to write once media. Notably, it changes the state of an alloy, rather than altering a dye.

Note that a manufacturer has produced a single pickup that will do DVD & CD. No, I don't know details about it.