Safety tips for handwriting
on Medical CD-Rs

CD-R and CD-RW discs are far more
susceptible to hand-writing damage than
DVD discs because of the differences in
the physical design of the discs.

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CD discs are based on a single piece of polycarbonate plastic. The CD-R and CD-RW media have the recording layers (organic dye in a CD-R and layers of metal alloy in CD-RWs) sitting on the top of the polycarbonate. A thin deposit of silver reflective alloy rests above the recording layer(s) in these recordable media. CD-ROM discs use aluminum as the reflective layer, but this “mirror” layer is deposited directly onto the polycarbonate base. Only a thin layer of protective lacquer keeps these metal mirror layers from contact with the air (Figure 1). In some discs an upper hard coating can offer additional protection, but the CD design is obviously susceptible to damage on the more fragile upper surface of the disc.

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Writing directly onto the fragile upper surface of CD-R or CD-RW discs poses two dangers: 1) damage to the mirror/data layer from excessive pressure of the writing stylus, and 2) damage to the protective lacquer surface from solvents used in permanent markers. Ball-point pens, for example, require pressure to roll the ball across the surface of the writing medium. That is no problem for paper, but the pressure across a CD-R can cause damage to the delicate layers below the disc lacquer. Figure 2 shows a CD-R written with both a ball-point pen and a felt-tip pen. On the right is an error map of that same disc. The image of the errors is flipped over so that the letters written by the ball- point pen show up as a combination of green (minor) and red (excessive) errors. There is no evidence of any increase in errors from the felt-tip pen.

Felt-tip pens require far less physical pressure because the capillary design of the stylus allows ink to flow through the felt onto the writing medium. The ink remains viscous due to the solvent that carries it through the stylus fibers. If the solvent is water, there is little danger to the lacquer surface of the disc; but the water-based ink may not be permanent on the surface of the disc. Alcohol-based inks also pose little risk to the lacquer surface of CD-R/-RW media, but there are other permanent markers whose solvents or acidic residue may eventually eat through the lacquer and expose the mirror alloy to air and to corrosion. Once corrosion alters the reflective capability of the mirror layer, the reading laser will no longer be able to retrieve data from the damaged sections of the disc. The pen manufacturers may have test data to determine whether or not the solvents used in their writing instruments affect CD-R lacquers. Memorex offers both alcohol- and water- based ink formulations in the CD/DVD Markers, and these formulations have been tested on CD-Rs with no problems. Some accelerated environmental tests have shown increased error rates in discs marked with even benign markers; so one should avoid writing directly onto CD-R/-RW discs that are meant for long-term storage or for high levels of temperature and humidity.