Since anyone who use this will be crafting a lot of mirrors, why not allow the "ingot" for mirror to be changed in config to serve as a balance tweak for mod pack builders?

Additionally if you still want to make it realistic, maybe give a broad list of materials allowed in the config, or let different materials produce different quantity of mirrors per ingot as a soft "restriction" and allow that to be changed in config.

Either case I think it will be a balance enhancement due to the sheer amount of mirrors people are gonna make.