I have recently run across "Amazing Molding Putty".
Spent a bit of time this afternoon making a mold of a scarab I have, then made a plaster support and then set about casting the first scarab with "Sculpt It". Time, about an hour with a great deal of that time just waiting for things to set up, things to dry. Now, just waiting on the Sculpt It to set up properly, that may take several hours.
Before this I have used a liquid latex material and found that if I purchased the smallest container (16 oz.), I would throw away 14 oz. of the product because it set up improperly in the container. So, with this new product, you mix equal parts of A and B and then mold it around the object....allow it set for 20 minutes or so and remove. So far I am impressed with the mold.