Tarbosaur/Gigantoraptor - Macroelongatoolithus egg clutch cast
As with most fossils, a considerable amount of matrix is still attached to the fossil. Usually this is to protect the fossil from being broken. For casting purposes this just creates too much mass to be reproduced economically and it detracts from the final cast. It must therefore be excluded from the cast. We usually do this by creating a hole to drop it into and them fill in around it to create a new artificial depth for the cast. The next step in the casting process is to created a frame to contain the silicone while the mold is setting up. We have begun to fill in dead spaces within the frame, around the fossil, to reduce the amount of silicone required to produce a mold. With silicone at nearly $1,000.00, wholesale, for a 5 gallon bucket you must do whatever you can to reduce expenses. As it was, this mold took about one half of a bucket. So, about $500.00 to make this mold.
The third photograph shows the silicone being poured onto the fossil. When you start pouring the silicone onto the fossil you must stay with it until you are finished pouring the mold. The silicone itself is white. The catalyst is dark blue. When the two are mixed together you get this nice Robin's egg blue color. The silicone is mixed up in batches of about 1200 grams at a time. It gets a little trickier with batches of less than that amount, because you don't want to mix up more than you need. If you have more than you need, you can't save it and use it later. The mixed silicone sets up completely within 24-48 hours depending on how much mass is involved. You do have several hours which can be used for the molding process, but once the silicone is poured onto the fossil you don't want to be removing it from anything which it has touched. This could create problems for producing a good cast.
The last picture shows the original fossil at left and a painted cast at right.
Original Macroelongatoolithus eggs
Eggs with mold frame
Silicone molding material being applied to eggs
Original clutch at left cast at right