A huge quantity of that plaque (thousands) were found in NY in the early-1990's in burlap sacKS and water damaged (brittle) and of no use to collectors due to breaking apart and, upon the inventry changing hands, it was suggested by some that their only salvage was to embed them as paperweights. Not sure if the example you show is part of that inventory or not.

Thomas C. Day explains water damage in his ANA articles in the MoGH.