Makin Molds Poll

[fembot]

I wanted to tap the knowledge of the board members out there and get their opinions on preferences on what they like to use when creating a mold. My husband is getting ready to start casting body parts (legs arms torsos) and we want something that is fairly durable so multiple copies can be made. I have seen people use plaster of Paris; which seems brittle. Bondo; which is durable but does it capture detail? And a few others which seem to be made of rubber or silicone, which doesn't seem to be very sturdy either. Any input would be appreciated.

[Tothiro]

Any mold material is going to have a mold-life of some length, nothing lasts forever. (to illustrate this some steel molds only yield a few hundred thousand casts).

The properties of your mold material should be determined by your choice of casting material. If you're casting something flexible, plaster is an option (though I wouldn't want to suggest it) but if you are making something rigid such as arms and legs in this case you'll need a flexible mold. Otherwise any keyholes will lock the part you're casting into the mold and you'll be left with a very time-consuming paperweight design.

Latex works but I don't like it - it deforms more easily and natural latex isn't as stable as silicone so it doesn't last as long.
Silicone can be ridiculously easy to use, there are also a number of tensile strengths it's available in, as well as "strengtheners" you might add. I've always used an off the shelf (or web page in this case) silicone with a four hour cure time available from Micromark.com. They also have a number of casting resins that are an easy 1 to 1 mix ratio, one of which cures in transparent amber and can be colored prior to casting by adding polyester liquid dyes or powdered dyes. I custom mix a flesh tone (taking into account that there will be a slight yellow addition because of the plastics native amber hue) so I can cast body parts in mego flesh tone.

Silicone molds, when just made a simple box mold with two, clam-shell parts, will usually yield between 50 to 75 quality casts. After that the mold will begin to weaken and may tear, or the details of the mold will rough or pit.
Resin plastic heats when it sets up, but not so much you'd need to worry about the temperature tolerance of the mold. Actually most silicones withstand up to around 400 degrees, so you could recast some low temp metals as well.

As for making mold boxes (to contain the liquid silicone when you pour it around the original as well as holding the halves together when you prepared to cast) I have stolen the common customizer trick of using Lego bricks to form temporary boxes - they're modular, easy to assemble and break-down and always the same size.

-Robert

[ctc]

Hmmmm....

I use GI1000 RTV silicone for all my molds. It'll last for at least 20 casts; more if you don't have a lot of fine details.

Don C.

[CrimsonGhost]

I would read up on the Smooth-On line of products. They are easy to use and you can get then in a number of varieties.