A cast is essentially a copy of a bone.  Sometimes it is called a replica.  The advantages of a cast are that it is lighter and stronger than real bone.  It retains all of the external details of the original specimens.


A two part mold can be made from an original fossil.  The bone is supported with clay and building blocks.
More clay is used to cover about half of the original fossil.



Once the molding rubber has completely dried, the sides made  of building blocks are removed.
After they are removed, the top portion (molding rubber and the original fossil)
 can be separated from the clay. 

Now the other side needs to be molded.  The first part that was molded is now placed on the bottom and the walls are built with building blocks to be high enough to cover the fossil and have some additional room.  Note that there is a bit of clay on the side in order to leave a hole to be able to fill the space that was the fossil to make the cast!

After the second half has completely cured, you separate the two halves! 

 The two sides are then put together and held together with rubber bands before the resin is poured into the mold.  The resin is then allowed time to cure.  Patience is important during this stage.


 Here is the final product, the cast on the left and the real fossil on the right.

 After painting, can you tell this is a cast?