Hydrocal

Sorry I have no experience with this material, but would love to know more!!

 

According to the book, Plaster Mold and Model Making. Chaney & Skee. 1973. Page 12:

[Gypsum cements] produce casts which are generally four or five times stronger than those made from ordinary plaster, but their use is limited to situations in which the plaster does not require carving and forming. The following is a partial list of these harder cements:

Hydrocal A-11* has a low coefficient of expansion, is smooth and hard-surfaced and is used in pattern-making for industry. This has a short period of plasticity and stiffens rapidly. It sets in about 20 minutes, at a consistency** of from 45 to 55.

Hydrocal B-11* also has a low setting-expansion, but has a high degree of plasticity and a gradual setting action. At a consistency** of 50, it sets in about 25 to 30 minutes; it is also available in a very slow-set version which takes about an hour, for use on very large patterns.

Hydrostone* is one of the very hardest cements and is used at a consistency** of from 32 to 40. The heavy, syrupy consistency cannot be worked in a plastic state and the set plaster is not suitable for carving. The mix sets in about 15 to 25 minutes.

Ultracal 30* is harder and stronger than Hydrocal, and it has the lowest expansion of all. At a consistency** of 37, this cement has a gradual set (about 30 minutes) and a long period of plasticity. It is used in pattern-making, and is also available in an even slower set, called Ultracal 60* (consistency** of 38).

* Trademarks owned by United States Gypsum Company.
** consistency refers to the water to plaster ratio, by weight, where plaster is always 100 parts by weight. For example, a consistency of 60 means 60 parts of water (by weight) to 100 parts of plaster (by weight).

http://www.usg.com/index.html
http://www.usg.com/industrial/art-statuary.html

 

Hydrocal is very heavy, like a stoneclay. I used to have a giant head my husband sculpted in it. It was very tough at that size but I'm not sure how tough it would be with thin walls on the edges of joints.

I'd see if they have a trial size of the resin to test it out.

 

I've used hydrocal a lot for nondoll sculpting stuff that needed reproduced. The surface of this is very hard and very smooth. It holds detail VERY well. It feels like a mix between concrete and plaster and works well if you are intending to use it with suspension, like stone dust, porcelain dust, walnut shells, or bronze powders. I have had to chip some of it off of a fragment that I intended to use for some jewelry so it was very thin. and it had marble dust suspended in it. I was easily able to nip away the portions I wanted trimmed off with some wire clippers and it had the look at the edges of long hardened cheese. It has an almost plasticy kind of give to it, it doesn't crumble, but sorta squishes away from the blade like softer plastics do instead of cutting neatly. I was afraid to use it for dolls because it does tend to be quite heavy, and also because I was afraid that it would warp slightly if tension was left on it because of how it gave when I tried to cut it. I may pour a few heads in it and beat them up to see how it behaves though. I have a good bit of it at my disposal.

 

I just did four batches in this a couple days ago. If you choose to use it, you have to use silicone molds with no release agent, only surfactant! we have about half and half at our studio and the molds that had the release agent in them caused little pinhole bubbles all over the smoother areas of the surface. It was a reaction to the release that you need to use for the rubber molds, where with the silicon, you don't need it with this stuff. For strength, you also need to interject some kind of aggregate. Sand, marble, something because this material draws strength from the filler and is not as strong without it. It is nonporous when it is fully cured and has a skin like a resin does instead of readily excepting liquids and dying easily like plasters. If you wanted to make a BIG doll out of this it would probably be OK but those areas that would be thinner would need to be scaled up so it would be strong or have armatures inside of them. the areas around the wrists where it is really thin would worry me. When I get a body completed I may try a couple pours in this stuff just to see how it behaves. I don't think a head would be a good example because I want to test the strength on a hand and wrist. I really think those areas would be problematic unless you made them chunky. I'll post a link to one of the finished pieces once I get them all set so you can see what this stuff looks like and the detail we are able to capture with it.