What to Mold creature Hand from?
Hey Gang,Hoping someone with experience in many different type of mold making materials could give me a better idea of what would suit this specific project needs best. Here is the purpose of this project and mold: Doing a test run for an animatronic hand. I've done the sculpture in Monster makers oil based clay, The goal is to have silicone skin that I can slip over the cable mechanisms and mechanical insides. I will only need to use the mold to create one to two skins (casts) and needs to be able to capture very high detail. Also I need to be able to put clay into the mold in areas that I need thicker and thinner for the "skin". pour in plaster to make a core mold, take the mold apart, remove the clay and float cast the final skin between the mold and the core mold (Hope I explained that clearly). I did some research and have watch most of the mold making lessons here and I'm not sure What would be my best option, I thought Hydrocal would be a good option but than I learned about Fiberglass molds and thought that might be better for detail, The main thing is I want to be able to capture all the details in the sculpture, the longevity and multi-use of the mold means nothing to me for this project. There may also be a better process out there I don't know about, so any advice is good.
Hope to hear your thoughts.
Comments
For a project like this I would normally do a 2 part fiberglass/epoxy mold with a core. But as you mentioned, you don't need to run a lot of pieces. If you are new to mold making, don't need to run a lot of castings, and want to save a bit of money, I would use something like Ultracal 30.
Hydrocal is ideal if you plan on casting in liquid latex, as Hydrocal is a bit more porous than Ultracal and helps liquid latex form a skin. But if you want to cast anything else I would suggest Ultracal 30 with a bit of hemp or burlap for strength.
This webcourse is a good place to start:
https://www.stanwinstonschool.com/tutorials/character-creation-stone-mold-making-tutorial
Just remember to reinforce the outer layers with something like hemp fibers or burlap.
Best of luck!
/Chris
Here are a few common formulas:
PRODUCT(S): Ultracal‚ 30 Gypsum Cement
CHEMICAL FAMILY: Mixture of Calcium Sulfate Hemihydrate
MATERIAL WT%
Plaster of Paris >85%
Portland Cement <10%
Crystalline Silica <5%
PRODUCT(S): USG‚ Hydrocal White Gypsum Cement
CHEMICAL FAMILY: Calcium Sulfate Hemihydrate
MATERIAL WT%
Plaster of Paris >95 %
Crystalline Silica <5%
PRODUCT(S): Duracal
MATERIAL WT%
Plaster of Paris >50%
Portland Cement >40%
Crystalline Silica <5%
PRODUCT(S): Hydrostone
MATERIAL WT%
Plaster of Paris >90 %
Portland Cement <5%
Crystalline Silica <5%
/Chris
https://www.facebook.com/1332645810/videos/vb.1332645810/10208570860532304/?type=2&theater¬if_t=video_processed
@Chris Ellerby thanks! I ending up doing a 1 to 4 mix by mass with 1 part cement all by rapid set and 4 parts plaster of paris. Did a few small test runs and it seemed to come out like a charm got a lot of detail and holds up well. Going to wait a few hours or even let it set up over night before demolding.
/Chris
Wish I could remember that.
But I really love your details with the veins etc.
Here is an example of a collapsable mold core that may help you a bit. This core breaks down so you can remove it when casting up a skin inside a 2 piece mold. If the core were solid (not collapsable) you would have to stretch or tear the casting to remove it, and possibly lock the mold up if not careful.
Hope that helps!
/Chris
You are a wealth of information
Alternatively, would slip casting work?
Thanks!
The hand is sculpted on a life cast of a hand/arm. That life cast can act as your mold core during casting as well (or be replaced with a modified version)
When you make the outer mold it should be designed to hold/support the base of the core so it will be positioned properly during casting.
This example image may help to visualize that. Just ignore that it's talking about a silicone mold, as you would want to use a stone or resin mold for casting silicone/latex gloves. The light peach colored piece would be the mold core. You can see that it has a wide base that locks into the outer mold so it always centers properly.
Also note the example video I posted above that shows how a mold core for hands can have removable fingers so it holds in place during casting but comes apart for demolding.
As far as slip casting goes, you can totally cast up latex (or even rotocast silicone) into the mold without a core. You just need the material to be thick enough to account for the thickness of your original sculpture, so the glove does not fit too loosely. But if you are looking to save money on molding and casting materials you could always cast up your gloves as a latex skin by dwelling latex in a stone mold, and then using foam padding to support loose fitting areas of the gloves.
How or if that coreless process would work depends on your sculpt though. But for a good fit, having a core is ideal.
/Chris