I think we all tried clay (works quite well for easy pieces or a quick copy), plastiscine (melts from the heat of curing resin), candle wax (same - ooch !
) latex (whew that stinks !)...
You should look for a chemist shop, specialising in modern stuff like polyester, PU, and other such products. Most (if not all) such products are
two component polymers.
There must be over a hundred such products, all "specially made for making modeling molds'". In reality, one is much better than the other. I suggest you look for a
silicone-based product. When you go there the first time, have a thorough discussion with the shopkeeper before you choose, and maybe show him some of the parts you would like to copy. Having a good relationship with him (her) pays off : there's plenty of tricks to learn... !
These products don't come cheap : often in the range of 10 and 40 USD per kilo.
What you should look for is a product that is still very flexible and can be stretched once it's hardened. Some dry quickly, some take up to 48 hrs to cure. I used to have a product of Voss Chemie (German ?) that was very good. Now I use something labeled "TinSil 30-70", but I'm less happy with that. There are hundreds. Brand names are often very local. If international, often they are still bottled by local chemists for the local market and still get a local brand name).
I tried four or five such silicones. Though I found a good product quickly, I looked further to find something that hardened a bit quicker. But those often are less flexible and stretchy.
Maybe ask to see a piece of cured molding-product. When you squash it with your hand, it should feel like a soft rubber ball, not hard.
The reason for this "soft" and "flexible" aspect is obvious : complicated parts that have little 'arms' or 'tentacles' in several directions, cannot be removed from a stiff mold without breaking. From a soft mold, you can.
Then just a few warnings :
- Always wear rubber gloves when you handle this stuff. Getting it on your fingers won't kill you, but it's a real misery to remove.
- Make sure you don't get it on your clothes, carpet,...
- When you smear it on any other object, don't clean.... just wait till its hard and it can be peeled off (when both parts are properly mixed).
- Storage. If you don't use it all, make sure you store the rest airtight, and away from kids !!! If you let it freeze, it's dead.
- This stuff must be mixed very thoroughly ! If you mix it poorly, parts will remain liquid. Believe me : you don't want that to happen to your model !!!
- Avoid air bubbles. What is air during the molding process, becomes a bubble of resin when you cast the copy - ruining the detail ! For this reason, a brand that cures very slowly is better. During the many hours when it's still liquid, many air bubbles rise. There are several ways to avoid bubbles, but the easiest and cheapest (but not with the best result) is to tap on the recipient that holds the mold or use a vibrator (or anything that serves the purpose of releasing the bubbles).
- DO NOT demold the original before it's fully hardened, all through.
All this is only on the product. Then of course there's a whole laundry list of instructions on
HOW to make such mold. I'll go into that next time.
I know all this sounds a bit complicated, but don't let that scare you. It's really worth trying. Start with copying a small, easy object (of which you have many) like a wheel, etc...
Copying resin kits is often quite easy : they were constructed specially to be molded. Copying plastic kit parts often results in a broken original and a useless copy, unless you're really experienced.
Does anyone have other tips on the choice of product (criteria) or specific brand names ?
