2-part Castaldo Quick-Sil rubber and talcum powder
Mix equal amounts of part A and part B, about enough to fill half of the mold. Work quickly, the working time is short.
Fancy adjustable wooden mold box. It has various sizes of blocks to fit the mold box frame so you can adjust the size and make smaller molds.
Push the mixed rubber into the mold box. Then embed the mini in the rubber. I also inserted a cork with a bit of brass rod to make the basic pour spout. I'll carve this a bit more if the first casts don't come out well and it appears to need a slightly wider opening. Brush on talcum powder (it doesn't take much) to lightly coat the rubber and the mold box near the rubber. This helps keep the next half of rubber from sticking too tightly to the first half or to the mold box. At this point you can also push something like the end of the brush handle a little into the rubber to make "keys' to lock the mold halves together better when casting.
Mix up some more rubber and press that into the mold box for the other half of the mold. You can see where I had to mix up a bit more and push that in on top of the rest. This works okay because the additional rubber will adhere to the other rubber.
Brush more talcum powder on to keep the rubber from sticking to the top of the mold box. Put the lid on the mold box and clamp it down tight. This squeezes the 2 halves of the mold rubber together so the halves connect firmly. I think it also helps squeeze the rubber into the details of the mini.
For the next mold I made I used some pieces of black styrene plastic I had around from making bases for the top and bottom of the mold box, and legos for the sides. The advantages of the legos are you can make different sizes of boxes, the rubber doesn't stick to the lego blocks and you can take them apart to get the mold out if need be. I made the lego mold box in 2 halves so it was easier to see that I had things centered in the mold. You still need to put some kind of release agent, such as the talcum powder, on the rubber to keep the 2 halves of the rubber from sticking together. I use a cheap soft hobby brush to brush the powder and blow off excess if need be.
The mold from the box and the mold in the legos after curing (probably less than half an hour later).
The molds for another base Highlander soldier and a Highland calf to go with the Highland cattle I did previously.The only thing left to do is trim the edges of the molds with scissors, carefuly pop out the minis and corks, and trim the pour spouts with a sharp hobby knife as needed.
The Hot Pot-2, for melting the metal for casting.
I'll do one pour and see how it comes out. Some molds, with no undercuts or slight ones, work fine as is. Others, with deeper undercuts or fine pieces like the muskets and swords I did before require "venting" (I think that's the correct term). To vent I cut very small channels from some part of the mold cavity out and up. I don't think the vents have to go all the way so the air escapes. Venting the mold for me is a matter of trying a very little, casting, trying a little more, casting, and repeating until I get mostly good casts. I think after doing a few molds you start to get a feel for where the vents need to be, how deep, how far, etc. The fewer and smaller I can get away with means I have to clean less of the cast piece after.