As a freelance sign designer I have the privilege of working with various sign companies and part of that is getting familiar with materials for ADA tactile signage.  From the basic budget engraving stock to photopolymer and to, what is now my favorite, zinc.  Because vendors charge by the square inch for zinc plaques it's a benefit to the customer for the designer to keep the size of the plaque small, just enough to provide the message and braille translation with the option to add a logo or graphic to the plaque.  To make my design packages more interesting I like to add layers of painted acrylic or milled finish aluminum to my plaques as center and back plates.  Again this is all taken into consideration when working with the customer's budget.  I've attached a couple of sample images that show some different finishes and aging techniques I specify for different projects.