I believe the pad is made out of printers gelatin.
Here are the instructions. I posted them in another thread earlier.
From Previous Post on this Thread
"Rub powered whiting into the cuts of the engraving to be copied, and wipe off the surplus. Press the engraving down on the transfer pad, remove it, and you will have the form of the engraving where the whiting was deposited. Daub a film of tallow on the piece that is to be engraved, and press it down on the transfer pad, over the whiting design. This will imprint the design on the piece. Several impressions can be made from each whiting transfer."
Sam please when you have it if you can post some photo of the process will be great,because i'm very curious about this tool, and i don't know if is for my little english but i can't understand very well how it work hehe