How to Cast a Nose Sculpture
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How to Sculpt a Nose - https://lifedrawing.academy/life-draw...
In this video, I will show you how to make a mold and cast a sculpture of a nose in resin plaster. Here’s the nose model we will get by the end of this demo.
In the previous lesson, I sculpted this nose model in plastiline. The link to this video is in the description. Now, I can use this wax clay model for mold making. To prevent silicone from sticking to the wooden board, I cover it thinly with a release agent. It is very important to check that this stuff doesn’t contain sulfur, which prohibits silicone hardening. I apply this waxy paste with a brush. There is no need in covering the whole board, only those parts that are next to the model. Also, I use the same release agent to grease the whole sculpture. Although it is unlikely that silicone would permanently stick to plastiline, I would better smear it to make separation easier. It is important to cover as thinly as possible to avoid visible brushstrokes on the model surface.
The next step is to prepare silicone. This kind of silicone for mold making consists of two parts, which have to be mixed in equal parts by weight or volume. Using some accurate scales with one-tenth of gram precision is the preferable way to measure. The part “A” is clear and I add 50 grams of it into the measuring cup. The same weight has to be added when it comes to the part “B”. It is green in color, which is probably done by the manufacturer to clearly differentiate between parts “A” and “B”. For some reason, the video camera doesn’t detect numbers on the screen, but I measure exactly the same weight as previously; so the mixing ratio is one-to-one. Two parts of silicone have to be mixed for several minutes. Make sure you scrape with a stick the bottom and walls of the container because if some liquid left unmixed, it would never harden. I will fast-forward the mixing process, but once again, take your time to mix silicone as thoroughly as possible.
I will brush-on mixed silicone with the same brush as used for smearing the release agent. It is a cheap synthetic brush, which can be cleaned afterwards with paper towel and turpentine. A strip of silicone on the board around the model is about half an inch wide. There is no need to make it any wider. This kind of silicone is rather liquid. It is easy to work with. Also, it hardens slowly, which gives enough time to brush it in a thin layer. As far as I understand, this tin silicone is engineered for pouring, not brushing; although the manufacturer does not provide much information apart from the mixing ratio. Anyway, I think it will be suitable for the purpose of mold making. The purpose of the first layer is to cover the entire model surface without any gaps and bubbles. It is better to do it with liquid silicone in a very thin layer. When the first layer will become touch-dry, I will build up the mold thickness by covering the model with several layers of silicone. Every layer has to dry a bit before applying the next one. It is important not to overdry silicone because the next cost won’t stick. Also, because this silicone is too liquid for brushing-on thick layers or applying it on vertical surfaces, I will add the thickening agent. This way, tin silicone will increase viscosity and become a paste rather than liquid. The thicker silicone will create an impasto effect, but it doesn’t matter because the first layer would hold minute details and polished surface. Here’s one important tip - make sure that the model’s nostrils are completely filled in with silicone. Otherwise you would have trouble with disassembling a hard mold when taking out the cast sculpture.
When the soft silicone mold is fully dry, I can cut off four edges, leaving about 8 millimeters of the shoulders on the board. For this purpose, I use a metal ruler and a very sharp scalpel. The scalpel glides easily through the silicone coat, which is about 3 millimeters thick. I did not build it up thickly because the model’s shape is simple and there is no need for a very robust mold. The release agent serves its purpose well and it is very easy to remove bits of silicone from the wooden board. Now, I want to test some mechanical properties of this silicone. Let’s see how much it can elongate without breaking. I can easily stretch 3 centimeters into 12, which is four times! This is very good. I also want to see how much force is needed to break this piece into parts. I can tear it with my fingers, but because it is very elastic, I think it will serve well as a soft mold.
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