Disk Depot

April 28, 2010

Why You Need Disc Pens

Author: disk depot @ 4:55 pm

Anyone who’s ever owned a CD, DVD or Blu-Ray (BD-R) writer will at some point have hand-written the label of a disc.

However, did you know that if you’re not using pens especially designed for the purpose, you may be risking damaging your data? Read on to find out why.

The Problem with CDs

The problem is most severe when it comes to writable CDs (i.e. CD-R and CDRW discs). To explain why, it helps to know where your data is stored.

The Layers in CD-R and CD-RW discs

Obviously the label- including any fancy design and overprinting- is on the top surface, and your drive reads the disc from underneath. So the data layer must be on the bottom surface- right? WRONG- in fact it’s very near the top, just under the label!

The bottom layer itself is simply thick disc of transparent polycarbonate that makes up almost all of the disc’s thickness (see right). When the drive reads or writes a disc, the laser beam travels all the way through this transparent layer before it hits the data layer and is reflected back by the reflective layer. Both the data and reflective layers are just microns below the top surface.

So the bad news is that if any damage gets through the very thin label layer at the top, it can easily cause further damage the reflective and data layers immediately beneath. If that happens, it’s bye-bye to your data.

Almost all CDs- including prerecorded (or “stamped”) audio CDs and CD-ROMs- have their layer at the top like this, but it’s obviously a bigger issue with CD-R and CD-RW discs as those are the ones you’ll want to write on.

So how does this apply to pens?

There are two main ways that unsuitable pens can damage the label- and then possibly the data layer beneath. One is that hard-tipped pens (e.g. ballpoints) can cause damage by scratching the surface. Here’s the video nasty showing you the gory details…

The other is that some pens contain solvents that can eat through the various layers. (Some people claim that the xylene and toluene commonly found in regular markers can cause such damage, hence claims such as “xylene free” or “toluene free”).The answer is to use a pen that has a soft, non-damaging tip and which doesn’t contain the damaging solvents. By this point, you’ve probably figured out that this is exactly what disc pens are for!

Disc Pens

Disc pens normally come in packs of four or so, usually including black, red and blue, and sometimes green too. Some also include a free “eraser”. (The eraser pen is normally coloured white and contains the same solvent as the inks in the other pens. This makes it easy to dissolve and remove the ink).

The problem isn’t as extreme with DVDs, which have the data layer in the middle, and BD-R/RW (writable Blu-Ray discs) which have it at the bottom. But why risk it when you can buy a pack of pens at very little cost?

Other points

If the top of your CD is visibly damaged, but it’s still readable, try to copy your data onto another disc or other media ASAP.

What happens if the underside of your CD is scratched? Ironically, you stand a better chance of being able to fix that by either polishing the scratches out or filling them in, since the data layer itself won’t have been damaged. (Scratches cause problems because they alter the direction of the laser beam). But that’s another issue altogether, and something we hope to come back to.

(This doesn’t apply to Blu-Ray discs, including BD-R and BD-RE, because in Blu-Ray the data layer is on the bottom surface. Fortunately, Blu-Ray discs come with an extremely hard coating such as TDK’s Durabis or similar products by manufacturers like Sony).

Further Reading

If you found this article really interesting, and want to know more about CD-Rs, we recommend the CD-Recordable FAQ.

Or if you’re bored silly by now, the important thing to remember is to treat your discs- particularly CDs- with care and always use proper disc marker pens when writing on the label.


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