If you Google how to antique a mirror, you'll find a variety of methods, many of which have you use muriatic acid which is a harsh chemical. (blog.jennasuedesign.com)
Use a solution of one part muriatic acid to 10 parts water (wear goggles when mixing). (homebuyinginstitute.com)
I use filtered water, hydrogen peroxide and no other chemicals except for muriatic acid to balance my PH. (healthylivinghowto.com)