WALLS, BARRICADES, RUBBLE, DRAGONS' TEETH.
First, you make a master of the thing you want to make lots of. You could make this out of almost anything, although I'd not recommend anything absorbent like card, because the latex can soak into that, and not peel off cleanly. I made my barricades out of lumps of modelling clay, with bits and pieces from my spares box stuck here and there. Build your master model on a flat surface with a lip around its edge. I found that the lid of an ice cream tub was perfect for this.
I had a go at making my own moulds out of latex, and the results have been rather pleasing. More recently, I have been using Gelflex too.
Next, get some latex, and paint it on. I bought my latex from a leather-working shop, where it was sold as glue. Use a cheap brush, and wash the brush immediately after use. If some of the latex does congeal on the brush, then you should still be able to peel it off with a bit of effort. Leave the latex for a while until it sets (may take a few hours), and then paint on another coat. You can get latex in a variety of viscosities. Go for the thicker end of the range, but not too thick. It should be liquid, not gunge. Too thick and it won't run into the detail on your model. Too thin and it will run straight off your model. One trick I found worked well was to paint on lots of latex, most off which ran off to form a puddle around the base of my model, and then to leave this for a while to thicken, and then to paint the thickened puddle over the model. This helps to build up the thickness of the latex layer. Another trick was to paint on a layer of latex, and then leave the model to dry upside down, with the ice cream tub lid supported at either end. This way, the latex congealed thickest on the peaks of the model, where usually it would run off and dry thinnest. I found that about a dozen layers was enough, but this depends on the thickness of the latex you're using, and the shape and size of your model.
|Here you see three masters of rubble, to be used for adorning the outside corners of ruins. The latex is white where it is still wet, and yellow where it has dried. The three masters lie on an ice-cream tub lid, which has a flat surface in the middle, and a lip all around to catch run-off. I have painted the latex not just on the masters, but also around each master, to form a wide edge to the moulds. Drying latex does smell a bit of ammonia, so you may want to open a window, but I find that the smell doesn't take over the room.|
|When the latex is dry and decently thick, you must decide whether to make a support for the mould. If the mould is small and simple then you could use it as it is without a support, in which case peel the latex off the master and use it. If it is large and will tend to flop out of shape, then before you peel it off the master, construct a wall around the mould (perhaps out of Lego, or perhaps just with sticky tape and card), and pour in plaster and allow it to set. This will form a perfectly fitting cup for your "glove" mould to sit in during casting. In this shot, you can just see the brick-pattern left by the Lego in the sides of the mould support.|
The sort of plaster you use makes a big difference. I started with the cheapest, and this gave me a quick-setting mix, with decent detail, and a lightweight finished piece. The finished pieces were also rather weak, though. I tried with other sorts, and some are very different. The more expensive powder took longer to set, but set with significantly better detail and very much tougher. There was another problem, though: the good stuff separated in the mould, forming a thick layer of plaster at the bottom, and water at the top. This meant that if I poured plaster in to the top of the mould, that the top part of the mould (the bottom of the finished piece) didn't come out unless I went back to the mould before the plaster was dry, and topped it up with more powder. If I had made my master models on little raised platforms, then these platforms would have created a well in the finished mould, which would have been useful in solving this problem.
The latex moulds I made a few years ago went stiff. However, I found that by massaging them under warm water for a bit, they recovered well enough to use. Even so, I should store one good casting from each mould in case I ever need to make another mould of the same thing.
Put the castings somewhere warm to dry, then trim the bottoms flat with a scalpel, or file them flat with a rasp, or, as I did, a cheese grater. You could then paint them. I'd recommend first sealing the surface with undiluted PVA glue. Into this I mixed cheap acrylic paint, the effects of which you shall see below.
The master models of the teeth themselves were made as follows. I cut four isosceles triangles out of plastic card, two much wider that the other pair. I glued these together to form a mould. I supported this mould with putty, and poured in a mix of moulding powder. I inserted a pin, head first, into the middle of the mix, and allowed the mix to dry with the pin sticking up in it. The pin served as a handle for pulling the shape out of the mould, after it had set. I then trimmed off the point of the pyramid with a scalpel. Using the same method and the same mould, I cast all the different sizes of dragons' teeth. The teeth are truncated rectangular-based pyramids.
The corner sections were made by taking an ordinary tile (which has fourteen teeth on it, in four columns: 4,3,4,3) and cutting it up into V-shaped sections. You can also see in this picture a destroyed section, made for games where engineers can blow things up. Again, I just converted a normal tile, rather than make a new mould.
|Gelflex is a soft rubbery substance I bought from my local model shop. It is a quicker way to make moulds than latex. I cut some of it up into lumps, put these in a small saucepan, and heated it on my cooker hob. All the while I stirred with a bit of wood, and wore safety goggles as the instructions advised. When the stuff had all melted, I poured it over the master, which I had surrounded with a retaining wall of Plasticine modelling clay. It bubbled for a bit, and then settled and cooled. I popped a lot of the bubbles before they congealed. The modelling clay gets very soft indeed from the heat of the molten Gelflex, and I found that with higher moulds (for pillars and the like) it collapsed into a messy puddle. I then made a surround using a sheet of pliable metal taken from a tube of tomato purée, which I taped together, and taped down to the work-top surface with masking tape. This worked fine.|
In theory, you can reuse Gelflex again and again, although I wonder if I will ever be able to bring myself to destroy a good mould and melt it down to make a new one. Since it is so soft, I imagine that the moulds will wear out fairly quickly, but unless I start casting commercial quantities, I don't see this as a limitation. I'm only casting a few for my hobby.