Interesting problem. You could include raised lettering giving a date of casting, but that might violate the terms of the trust. Or, you could dissolve a dry pigment such as a yellow or red ochre (a cheap and common earth color) in a little water and add it to the plaster before making the cast. The pigment will alter the drying time, but that shouldn't be a problem. This will probably work alright if there are no undercuts. The safest way would be to make a mold of the original and cast your new plaster in that. Remember that you need a release agent (soap works well) to allow you to separate the two pieces. The more I write, the more I hope you have someone who is an experienced plaster caster doing this for you.... Good luck. Jack C. Thompson Thompson Conservation Lab Portland, OR [log in to unmask]