D. Dyes for Resin.
1) Opaque pigments are also available from TAP or any resin supplier. We find that using a combination of white and gray opaque pigments produces a very good neutral gray color cast that is excellent for viewing and photography.
http://www.tapplastics.com/shop/product.php?pid=50&
I'm assuming you have access to a fume hood? All of these materials are toxic so you'll want to work safely.
2) "And a by the way: I recently learned that all acrylic paints are not
created equal. I often mix acrylics in with epoxy to color a cast, and
a cheap hobbyshop brand I thought I could save some money on (Delta)
reacted horribly with the epoxy -- lots of foaming and smoke. I'm
sticking with TAP colors from now on. "
E. Separators.
1. Silicon and Epoxy Resin. IIRC, epoxy resin separates OK from silicone without it, but I want to minimize any potential breakage of the bones. I'm guessing that an aerosol one would work best to prevent fine details from being filled in by the separator itself. Does anyone have a favorite brand?
2. Be very careful with your selection of "universal mold releases" and be aware of the specifics of materials that can cause cure inhibition. Platinum- and tin-based molding compounds have very different sensitivities to various materials that can cause cure inhibition. For example, many platinum-based compounds are inhibited by contact with tin-based rubber, epoxies and oils. Also, some mold releases, especially silicone-based, are intended only to release plastic resins from silicone or latex molds, and are NOT designed to come into contact with un-cured silicone molding compounds....in which case they may cause either cure inhibition or fusion (as in adhesion, not nuclear).
Not all commercial separators/releases designed for silicone molding compounds contain petroleum jelly. Check with the manufacturer.
Finally, I'm not sure why a release agent would be necessary, especially if you are going to apply Krylon first anyway. I've not had any problem with tin-based silicone molding compounds adhering to latex or inhibiting even without a barrier or release. Haven't tried platinum-based with latex. Tin-based compounds (condensation-cure silicone rubber) are far less sensitive to inhibition than platinum-based (addition-cure) compounds, so all other things equal, those might be the better choice.
There is a decent manual/catalogue that gives details of various molding compounds that is available in pdf format from the Polytek website, and their tech people are pretty good about responding to specific questions. Of course, other manufacturers offer similar support.
Regardless of the choices you make and the advice you get, be sure to test your materials and techniques on a small scale before committing!
F. Silicone and Latex.
1. As for keeping your latex from sticking to your silicone molding compound, I've dealt with that before using a spray-on universal mold release. In some instances, I've also applied vinac to the latex before pouring on the silicone. This is how we like to keep silicone from sticking to silicone, and it works on latex too.
2. Obtain. KRYLON Make It Last Clear Coat Sealant Spray” –this is the closest to the name “Clear Coat”. It may be Acrylic like Krylon® Acrylic Crystal Clear.
3. Usually, water-soluble parfilms are used to coat latex, and act as an approporiate barrier against binding with silicone. Anything petroleum-based can damage latex. Polytek makes a clear parfilm, I believe.
II. Making Silicone Rubber Casts from Latex Molds and Vice Versa.
1) I have been pouring silicone pour spout plugs into latex molds for years -never had any trouble. The main issue is that the separator commonly used for silicon is basically petroleum jelly - even the commercially available spray separators are thinned out pet. jelly. Latex exposed to petroleum products will soften and swell, although I'm not really sure petroleum jelly would have that much effect. I always spray a couple coats Krylon clear acrylic on the latex, letting the first coat dry before applying the second. Then you can use a thin coat pet. jelly without it getting on the latex.
2) To start off, I want to say, I've not ever done what you want to do. But that won't stop me;)Before starting this project, I would:
1. Wash the endocast of latex in a lukewarm, slightly sudsey solution of Palmolive green (pretty much unadulterated/no-unknown-additives soap), using a soft brush in a circular motion, not a hard one like a toothbrush--something a little stiffer than a baby's hairbrush. How old the latex is will determine the surface integrity. I would design the mold as if the endocast were fossil/rock, with no give. Meaning no deepish undercuts.
2. If you use a really serious barrier material the compatability issues go away. My inclination is always butvar 76 by default, multiple (6-10?) thin layers (the butvar in a very thin solution of acetone). (I hate vinac because it becomes like mucus when trying to remove it and it never comes away cleanly, and usually some of the substrate migrates. Like a fragment of bone.)
3. Spray well* (lightly, twice, allowing 20 min. drying time between sprays) with a universal mold release (compatible with both latex and silicone). You can get this online at artstuf.com the website of Douglass and Sturgess. They'll ship.
*I put the mold/object to be molded, on a turn table and spray lightly from four directions. Too heavy a coat of separator causes a shiny cast, which is harder to look at (study), and misrepresents the original.
And if you:
4. Don't let things sit around between steps for too long (?) it should work.
The worst that can happen (preparator-think, one of the crucial first steps of any procedure to be undertaken) is you have to clean off the uncured molding material using acetone with paper towels and swabs. Which probably won't hurt the latex for a once or twice, quick exposure. It might harden the surface of the latex, which is a not unuseful attribute for your purpose.
III. General Casting Comments for Large Casts.
The larger endocasts you mention may not be suitable for solid casting in either epoxy or casting resin...both reactions are quite exothermic and heat may pose a problem. Silicone RTV can withstand considerable heat, but we generally avoid making solid resin casts of anything 6 inches in diameter or larger. The easiest solution for the larger casts might be plaster or gypsum cement unless you are willing to use hand-layup or rotational casting techniques.
2) We've had good success using this silicone with the urethane casting resins. The molds can handle some heat, but with repeated castings they will tend to become more likely to rip and tear. Keeping in mind that the greater the volume is, the hotter thetemperature will get can help you to decide what methods and materials are best for castings. If it is a huge volume, a layed-up hollow cast (subsequently filled with urethane foam) is a better choice. It also seems that molds made without the thixotropic are stronger, perhaps because they cure more slowly. We often put layers of cheese cloth into our silicone molds to help with tear resistance. I hope this helps you out. As pointed out earlier on this thread, there are many correct ways to mold a cat!
THINGS NOT TO USE.
Dyes for Resins
Dyes for some craft resins are not opaque - you want a pigment.
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