Do all discs have a hard-coat covering or some equivalent thereof?
Yes. Because data is so close to the surface, the Blu-ray Disc specifications requires some variation of hard coating be applied to every disc. The Blu-ray spec has a minimum hardness rating the disc has to achieve to survive normal handling by humans. A hard coat is one approach to achieving the hardness spec. Individual vendors can take different approaches (for example, a hard-coat spin coat on the disc’s surface). As mentioned earlier, with Blu-ray Disc, data is stored close to the top surface layer. The top of the substrate is.1mm beneath the cover layer surface, which means the substrate itself is 1.1 mm thick. “A greasy fingerprint could be destructive, since you’re focusing so close to the fingerprint,” says Parsons.
