Sunday, September 9, 2012

05 Molding Design Nº 10

The other way to make a mold is to find the parting line on the doll part, support the doll part on pads of clay to make the parting line as horizontal as possible, then build-up a clay bed from the molding board up to the parting line. In this photo, the parting line is red, the first clay bed is green,  and the first half of the moulage mold is cyan. Click on an image to enlarge it.

The parting line must be found around all the fingers and the thumb.

When making a clay build-up for pouring moulage, it is  a good idea to place clay registration keys on the clay build-up. This is because it is difficult to carve registration keys in moulage. A parting agent is not needed between moulage mold halves because moulage does not stick to moulage. A moist moulage mold will not stick to cast carving wax. Casting carving into a moist moulage mold is very similar to ccasting carving wax into a water-saturated plaster rough shell mold. The difference is, the moulage is reusable.

One nice thing about making a moulage mold is that the moulage is semi-flexible, so if a slight mistake is made when drawing the parting line, the oil-clay model will not be locked in the mold half. The moulage may be slightly flexed to release the model. After making the oil-clay build-up, pouring the first half of the moulage mold, and letting it set up, the mold is flipped over and the oil-clay support pads and clay build-up are removed in order to pour the second half of the moulage mold. This is the same procedure that is used to make a multi-piece plaster mold, or multi-piece silicone rubber mold. The oil-clay model is always left embedded in the clay build-up until after the mold material has been poured. Registration keys are always made for each section of the mold.

One thing I am considering to do is to cut off the hand and mold it in its own mold. Since I have decided to make a one-piece block mold for the arm, cutting off the hand will make it simpler to cut the mold with a mold knife. I may make a simple two-piece moulage mold for the hand. Because the hand is small, the clay build-up will not have to be very big.

For an example of making a two-piece moulage mold with a clay build-up, please look at this post about molding a ball for a joint, from July 16, 2011.

One important thing to remember is that if you are making a clay build-up for a silicone rubber waste mold, be sure to use a sulfur-free clay. Evidently, sulfur inhibits the curing of certain silicone rubbers. I am not a chemist, and I do not remember which silicone rubbers are adversely affected by sulfur, so my solution is to not use any clay containing sulfur when making a silicone rubber mold. Fortunately for me, the Roma Plastilina which contains sulfur is a green color, and the Prima Plastilina which is sulfur-free is a tan color.

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