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Research Topic: How to Destroy a CD-R

Question: How do I turn a CD into an unreadable coaster?

Answer: If all you want to do is prevent the CD from being read (rather than actually making a coaster) do not attempt to fold the CD in half. Some CDs use polycarbonates that will shatter dangerously. Read below for safer methods.

By Bob Starrett ( [broken link]), 22 March 2000.

It's easy enough to get data onto a CD-R disc, but what about getting it off? What if you have old backups or other data on disc, and you're afraid that if you simply throw the disc into the trash, someone will pick it out and have access to your valuable data? Destroying CD-R media is easy and fun, and there are several ways to accomplish the task, but always keep personal safety and the environment in mind.

Remember that a CD-R consists of a clear polycarbonate disc, with dye on one side and a reflective layer on the other. If the reflective layer, the dye, or the polycarbonate is sufficiently damaged, the disc cannot be read. So, one of the easiest ways to destroy a disc is to physically damage the polycarbonate itself. Simply cut the disc in two with scissors or a paper cutter.

NEVER try to destroy a disc by bending it between your fingers in an attempt to break it. Some will bend, but not break. Some will break in two. Some, however will shatter into flying shards of polycarbonate – ouch! This is dangerous, not only to yourself, but to any spouses, children, or pets which happen to be in the immediate vicinity.

Cutting the disc into two or several pieces is a quick and easy solution, but if you are really paranoid, you have probably already guessed that those crafty folks at the CIA and the FBI can probably put this disc back together and read most of the data off of it. Recently a man was convicted of murder, partly on the basis of information contained on a floppy diskette that he thought he had destroyed by cutting it to pieces with a scissors and crumpling it up. The FBI was able, through a rather elaborate process, to reassemble that disk and retrieve the incriminating information from it. (Interestingly, he smuggled a pair of scissors into the interrogation room and the cops handed him the actual disc - and that's when he cut it up, right in front of them. How embarrasing.) CD-R is not far behind for the FBI, most likely, so leave the details of your transgressions in your head, not on a disc.

So, for the paranoid, or those whose data is truly sensitive or secret, we can move on to other levels of destruction. One effective, but not necessarily recommended, method of destroying data on a compact disc is to zap the disc in a microwave oven. It takes only a second or two to render the disc useless, as demonstrated here: [broken link].

[I think Bob missed the point of the page referred to here. After microwaving the CD it was placed on top of a Tesla coil. Oh yes. That's when the fun really started. More useful for the home CD chef is [broken link] - Ian.]

However, this method is not recommended for the general public, because it may damage the microwave, and it is unknown whether the byproducts of the meltdown may remain in the oven and subsequently contaminate any food cooked in it.

Destroying the reflective layer is effective and all too easy, as any of us who have tried to remove a sticky label from a CD well know. The reflective layer is thin and delicate. To demonstrate this, place a piece of duct tape across the top printed portion of a disc and pull it off with a quick jerk. Now you have gold- or silver-colored duct tape, and a semi-clear piece of polycarbonate. However, even if you remove all of the reflective layer, it is likely that the spooks at Langley or the sleuths in the Hoover Building could still find a way to replace the reflective layer and read data from the disc.

If you are not really concerned with security, but just want to quickly make a disc unreadable by the average person, you can destroy sector 16 of the disc. Sector 16 contains the disc's volume descriptor, and is necessary for any CD-ROM drive to be able to read the disc. How do you determine exactly where sector 16 is? Well, if you imagine the structure of the disc, you can get a good idea. Since a disc has approximately 333,000 sectors, usually a few more, but never less, and these begin at the center of the disc and move outward, sector 16 is pretty close to the center of the disc, within an eighth of an inch of the beginning of the writable area. Just take a car key or other sharp object and scratch a quarter-inch line across the beginning of the disc, on either side, or both. Now, with sector 16 unreadable, the disc is unreadable under normal circumstances, although the remaining data is still intact.

It's a little harder to destroy a pressed CD completely. Since the data, as represented by the transitions between the pits and lands on the disc, is physically stamped into the polycarbonate, removing the reflective layer still leaves the pits and lands intact. The only way to truly render a pressed CD useless is to remove the pits and lands physically from the polycarbonate. While you can buy a special CD destruction device for about US$6,000 (hand operated) and the motorized version for about US$11,000, the budget-conscious among us will surely opt for a cheaper solution. There are a couple of quick ways to make a pressed CD, or a CD-R for that matter, useless. Take it out to the sidewalk and throw it data side down; put your foot on top of it and rub it around for a bit. That will do the trick for most purposes. Tossing it on a belt sander has the same effect, but watch your fingers.

Sometimes we have enough trouble making CDs that it's hard to imagine wanting to destroying the results of our hard work. But there are times when data needs to be destroyed, and the methods mentioned here are only a few of the many ways to intentionally ruin a CD. Remember that there is a difference between making a disc unreadable and completely removing the data. Use the method that is appropriate for your own security purposes. Think a little and you will come up with some intriguing methods of your own. But remember: Safety first!

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