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On 23/08/04, Jerome Hartke wrote: > "Color" in the polycarbonate layer relates to the visual part of the > spectrum, while the CD laser operates near 780 nm in the > near-infrared. Consequently, the visual properties of the > polycarbonate are immaterial. Yes, but when a dye absorbs strongly in the red there is a chance that it will also absorb in the near infra-red. Do we know the spectrum of this black dye? Visually, it has the same purplish hue as the dye used in markers. It may be the same. > Modification of the infrared properties > of the polycarbonate would degrade the read/write capabilities of the > disc, and is not done. It would reduce the sensitivity. So does the anti-halation dye in a film. That also increases the resolution, which is the issue here. The advantages I am suggesting are possible (not necessarily actual as I have seen no scientific tests) are 1. better resolution - i.e. more accurate lengths of the "dashes" written on the disk 2. reduced action of light on the disk (causing ageing) > > I do not pretend to be always right, but the above information is > accurate, as a bit of common-sense thought would confirm. Common sense can be misleading. Regards -- Don Cox [log in to unmask]