This post spans over a few days. Making a silicone rubber mold takes time. How much? At least the cure time for the silicone rubber you use. Add to it the time it takes to prepare the mold. Let's also not forget you double all that when you make a 2 part mold.
The cat head I am making a mold of will be a 2 part mold. I could probably do a 1 part mold and slush cast the resin, but I prefer to do a 2 part mold which gives a more consistent thickness.
I used magnets for my keys and the wall is foam board.
One part is done.
And here are the 2 parts of the rubber mold finished.
A side-by-side comparison of the original cat head and a resin cast head. The original polymer clay head weighed 26.1 grams while the resin head weighed 21.9 grams.
There are some slight imperfection with the teeth and the back of one ear. I have to check the mold to see if it was a one time thing or if some epoxy will be needed to do a minor fix.
I used Smooth-On Dragon Skin 30 for making my silicone rubber mold. I used 8.4 oz of rubber for the first half and 5 oz of rubber for the second half. The cure time is 16 hours for each part and I used 50 psi in the pressure pot to get rid of the bubbles. Although you can use OOMOO 30 without a pressure pot, the results are better with a pressure pot. The Dragon Skin 30 you NEED a pressure pot. Even if you try to mix carefully, bubbles are created. This stuff is thick to mix when compared to OOMOO 30. And it costs more too. :)
The resin I used was Smooth-Cast 305. For the first cast I mixed 2 oz of resin, which was too much. The second time I mixed 16 grams of resin, but that was too little. So the third time I mixed 25 grams which was still just border line. In the future I will aim for 27 grams. I have to take into account extra resin that is left in the cup, syringe, and resin needed for the vent and pour hole.
I should probably make the paws next instead of giving into the temptation of painting the resin head.