Shocking Truth about Thin-skinned CDs (or why you should never write on a CD with a Sharpie)

I’d heard the adage that the top surface of a CD or DVD is thinner and more fragile than the bottom surface, but until I went on a cleaning bender, I didn’t get it. I reallly didn’t get it. It’s true, it’s true– the top layer of CDs and DVDs are thin. Shockingly thin. Here is a photo gallery of the CD that taught me just how fragile a writeable CD is.

After the holidays, I went on a desk and home office cleaning frenzy. Under a pile of papers, I discovered a disk that failed when I’d burned it. (also known as a “coaster!”) 

“Oh bummer,” I said. “A Bad CD. What’s it doing here? I should toss it out.” Then I remembered that I’ve wanted to destroy a disk just to see how it was put together. “Allrightie, then! I’m going to break this lil’ puppy!” I began to bend the CD. I figured that it would soon snap, but it bent and kept bending. At the crease, I noticed that a ripple appeared. It looked like a buckle or oblong bubble in the rainbow foil.

Strange! What is that? I bent the CD some more, then dug at the bubbly area with my fingernail. The top surface peeled away, exposing the clear plastic disk beneath.

No. No! Is that all?

I tore off a little bit of that flimsy layer and held it between my fingers.

THAT is where the data is? That’s the surface that the CD or DVD laser writes to? Yeah, I’d heard that the top surface is fragile, but until I peeled off that layer of the CD data writeable rainbow-metallic layer, I never know how fragile.

I took several pictures to try to convey how thin-skinned the top of a CD is.

Now think about your typical Sharpie pen. I use ’em for sign-making, I use them for other writing. In days of my past, I used to use them to write on CDs after I burned one. I stopped doing several years ago, once I learned that permanent markers are a dangerous thing:

Think about the smell of a standard Sharpie permanent marker pen. That tell-tale whiff (pee-yoo!) indicates the presence of solvents and chemicals that come into contact with that very thin media layer. Will they dissolve the layer and eat down into the place where your bits are? Could be. Do you want to trust your data CDs and DVDs to Sharpie solvent while you wait to find out?

Yes, I write on my disks, but I use pens formulated to be safe. These are Staedtler Lumocolor CD/DVD markers. And my handy stack of CD envelopes.  The pens I now use are different, the ones that say that they’re formulated for CDs and DVDs. I have some Staedtler Lumocolor CD/DVD markers. Picked them up at a drug store a few years back. Now I don’t see them offered for sale, it looks as though Staedtler may have made this available under a different product name. There IS another option, though: Delkin Archival Gold CD/DVD Safe Pen Solvent Free.


Why are CDs so fragile? There are two types of CDs. Mass-produced CDs (such as commercial software disks and commercial Audio CDs) are structured differently than CD-Rs (the types of CDs you burn yourself).


Side view of a CD (compact disc) manufactured by mass production, compared with side view of a CD-R (where you burn CDs one by one). The manufactured disc has a reflective layer that contains actual indentations that the laser reads, whereas the CD-R has a dye layer that's changed by the laser.  The way that CDs and DVDs work is that a laser reads the underside of the disk, detecting teeny indentations. In the case of mass-produced CDs, the indentations are physically present, in the form of extremely tiny pits in the reflective surface. On CD-Rs and DVD-Rs (and DVD+Rs), there’s a reflective surface embedded in the disk, and a dye layer below it. In an unburnt disk, the dye layer is completely transparent, or 100% reflective. When you “burn” a disk, the laser hits the dye layer, and that spot the dye becomes opaque. There are no physical pits, but a dye layer that’s opaque in some places and transparent in others. The laser reads it back, and interprets those transparent/opaque parts as bits, or data.


(If you want to know about how CDs and DVDs work in more detail, here are two places that go into matters in more detail.)

Recommendations

Now that you know how fragile CD-Rs are, What should you do?

  • Do not use Sharpies or other permanent markers to label your disks! Use markers that are marked “safe for CD/DVD”—they don’t have solvents. Make sure by giving them the smell-test. If you smell that permanent marker chemical, do not use them.
  • Also: No ball point pens.
  • Do not stick a label on top of a disk. And, whatever you do, if a label is attached, do not detach it. Make a copy of the disk instead on a new disk. No stick-on label on the new disk, either.
  • Keep your CD-Rs and DVD-Rs away from dust. Keep them in their plastic cases, or inside a paper envelope sleeve.
  • Oh yes, and avoid excessive heat and humidity for your disks, too.
  • Store disks upright (like a book), so that disks are on an edge. Do not store them flat.
  • Don’t fold or bend your disk. (Unless it’s a bad burn and you want to see what happens to it, of course)
  • When you burn a CD or DVD, burn two. Redundancy is your friend. Redundancy will ensure that you keep your data. If one fails, you have a second one. Lots of Copies Keeps Stuff Safe. At Rootstech, during the Saturday morning keynote, Brewster Kahle (of the Internet Archive) talked about the major problem—most of our software is rotting. One thing he alluded to without mentioning it is that LOCKSS   LOCKSS principle—Lots of Copies Keeps Stuff Safe. The Internet Archive not only exists in the Bay Area of California, but in Alexandria, Egypt and partially (a copying work in progress) in Amsterdam. Use the same kind of redundancy with your data. At minimum, burn two copies. If you want, store the other copy in another location.

P.S. Why was the Audio Compact Disc given a capacity of 74 minutes of music? 74 minutes is the length of Beethoven’s 9th Symphony. Sing your Ode to Joy over that, people!

To Come in a later entry: What is the best CD?

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Posted by Susan A. Kitchens on February 22, 2011 in • AudioAudio: HardwareDigitalityLongevity
4 CommentsPermalink

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Comments

Great article Susan!  I had no idea they were THAT fragile.

Joan Miller (Luxegen)  on 02/22  at  03:56 PM

Great writeup, Susan. I’m always beating my clients over the head with this stuff but sometimes people have to learn the hard way. This is another reason that I’ve standardized on using inkjet-printable Taiyo Yuden CD-R and DVD-R blanks. That extra layer of “paint” on the top of the disc adds another bit of protection to that flimsy aluminum layer below.
Dave

Dave Morrison  on 02/23  at  02:59 PM

One very important thing to consider is a type of CD-r, the cheapo discs shown here, with reflective surface on the top (like a mirror, no marks or additional writings) are without a doubt the worst and most fragile there is !!!!
AVOID THEM AT ALL COSTS !!!

I found that a hard way when trying to play my old ps1 games bought as copies 10 years ago, and today 90% of that type discs simply won’t play, looking at them at light often could see small spots of cd rot.Often there are spots near the middle so thats why it won’t start them at all.
The good advice here in comments is to use some type that has xtra strong top surface, like the ones for printing.Also there are some that resemble the gamophone record on the top, they are also reinforced…

Miky  on 01/20  at  06:45 AM

Miky, a shiny top of disc (looks like a mirror) does not, by itself, indicate the quality of the disc.

The highest-quality gold discs that I get, MAM-A (or Mitsui Gold), come with a nice shiny gold top surface with nothing on it. Same for MAM-A/Mitsui Silver. High quality, no label or printing on top.

I grant you that the extra layer of substance on top, for printing, does add more protection.

Also, the type of dye layer is more an indicator of quality. And the manufacturer.

I need to go back to the disc in question, but I think I bought a set thinking that the manufacturer was more reputable, and (possibly) found out later that it wasn’t as great as I first thought. It’d take a bit of research to do.

Still, it’s matters like this—and uncertainties—that underscore my point about redundancy. Burning discs? Burn two.

Susan A. Kitchens  on 01/30  at  11:16 AM

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