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The reading laser has no effect on any DVD disc because its power is too low to heat any material. All DVD discs are molded or pressed in injection molding equipment. The difference is that movie discs have the data pits molded in while recordable discs have only tracking guides (grooves, modulated signals, pre-pits, sectors, etc.) and disc identification molded in. That's because the "data pits" for recordable discs are made by burning organic dye (CD-R, DVD-/+R) or by melting metal alloys (CD-RW, DVD+/-RW, DVD-RAM) to make dark marks that resemble light deflecting pits.
An aluminum layer is deposited on video discs and rewritable discs to act as a reflective mirror layer. In dye-based media it is silver alloy or gold because the dye is corrosive to aluminum.
Aluminum and silver alloys are subject to corrosion if air or sulfur-bearing water particles reach the metal. All dyes eventually degrade over time in the presence of heat and humidity and high levels of light (Laser light is only one wavelength tuned to the dye). That is why errors increase over time even in "perfect" discs.
There are nearly 80 different test criteria for DVD discs to determine quality. Quality is generally due more to processes than to materials used since most manufacturers use nearly identical materials in most cases. The geometry of the grooves in the molded plastic is a vastly underrated parameter. Dye coating uniformity and integrity and the purity of the metal alloy targets are the next most critical steps, but there are hundreds of steps that have to be just right to yield an excellent disc.
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