I would suggest wiping off what mold you can and then run some mild temp water with dish soap and lightly massage both sides of the skin under the soapy water, removing the mold and loose scales. Then rinse off both sides with cold water and lay flat on a board and pat it dry with a clean cloth. Lastly, let it dry on the board for a couple days, flipping after each day, until it's dry. It will draw up on you a bit but the remaining scales should flake off with a Popsicle stick or soft tooth brush. Before you cast it, wipe it with some denatured alcohol to clean off any soap residue, and you should be in business. Just becareful not to soak them too long or the skin with get very fragile and tear easily. Good luck!
