Fetal Deep One Moldmaking and Casting 02

So last time, I told you about a tight seam line. Here is a magnified picture of a small area along the spine. The cleaner this line is, the smaller the seam will be which translates to less cleanup after. Attention to detail during the mold making stages is savings in work later.


These are the limbs with sprues attached in little small boxes of clay. The sprues are those little conical towers. A sprue is the part of the mold where the material is going to be poured into and continue on towards  the actual mold surfaces. They are molded into the model so it will be one piece. There will be a piece of plastic after casting which represents the sprue itself but that gets cut off the casting and tossed.


I changed my mind on the type of mold i wanted so i had to rework the walls on the body mold. The walls are now lower and closer to the model. These walls will act as overflow stops for the silicone rubber. At first, i wanted a block mold, meaning a big chunk of rubber with enough mass to hold its shape without distortion of the inner mold surfaces. Instead, i decided to do a thinner mold and use another outer stiff mold to support the thinner inner one. This outer mold is called a mother mold.

This the first half of the body of the model before the silicone. I am showing two views because top down can be confusing without some idea of depth.



This is the first layer of the silicone. Initially, it is put on very thin. I use a brush to be sure i get into every nook and cranny. The layer is kept thin which helps the bubbles to dissipate. As long as the important surfaces are well covered, i have no problem filling the outlaying areas by pouring the silicone rubber into the mold. This is done by holding the cup a bit above and allowing the rubber to be poured in such a way that a thin ribbon forms. This ribbon will not carry bubbles. This is poured into one corner and allowed to proceed on its own along the paths available. Those bubbles at the top area are where i dumped the a bit of silicone to show what happens when not following a good technique. Where they are means nothing but if they were against a surface of the model that would be bad. I dissipated them with a brush afterwards.


When the silicone is sticky but not leaving itself on the fingertip of the glove, a second layer is poured. This is  generally somewhere around 45 minutes to an hour. This time a thickener is added to the silicone which makes it act like cake frosting instead of a liquid. Simply spread with tongue depressor and serve in twenty minutes…..The small green piece of clay is a test of another type of clay to see if it is amenable to silicone.


The small parts (limbs) were done with an initial thin layer of silicone followed by a simple pour of more silicone about an hour later.



This is all now going to sit overnight and let the chemical reactions proceed. Next time, we will see things from a slightly different angle.