Project - Using Rigid Moulds:
Rigid moulds are easy to use if you follow a few simple tips. First, always dust the mould or the polymer clay (or even both) with a fine layer of talc or cornstarch as a release agent. I know I keep repeating this, but it's important because without it the clay will stick to the mould, making it almost impossible to get out without stretching your moulding to an almost unrecognizable state. More importantly, you may leave tiny scraps of clay in the mould, which will either block up detail or get embedded in your next try. These scraps can be tricky to remove, as you don't want to use any hard, fine tools (risk of scratching the mould). If this does happen, try tapping them with a small amount of very soft clay in the hope it will pick up the scraps - it probably will after a few tries, but it can take an irritatingly long time to get the whole thing properly clean again.
If the mould is deep, or has deep parts, such as the nose on a face, make your clay into a carrot shape, and press into the mould with the point going into the deepest point first (see picture at right). The deeper the mould, the longer and thinner the shape should be before you put it in. Of course, if your first moulding doesn't come out well, you can always squash it up and try again.
With a rigid mould, the mould itself is often flat on the top surface and is usually hard enough not to be cut with a craft blade, so you can cut along the surface to flatten the back of your moulding before removing it. If you do that, leave the clay to rest for a minute or two in the mould before easing or knocking it out, as it will stiffen up a little and make the removal easier. I prefer to use much more clay than required in the mould, though, and use this excess to pull out the moulding. I then use a long flat blade to cut the moulded piece off of the excess.
This doll at the left was made in a commercial mould from Amaco and as you can see I made the separate parts in different colours, but didn't do different colours for the details. You CAN fill each area with a different colour, but I find it hard to prevent them smearing together when you press down to get a good moulding. Another way is to mould each part in several colours, then cut away the parts you want in another colour and replace them with those parts from one of the other mouldings.
Clean the release agent off of the clay where you want two parts to stick together, and roughen the surface, then press them on firmly. Bake, and they should be fixed. A little clay dilutant or liquid polymer clay can help them to stick, if you have troubles with this.
If you prefer to just mould partial colours, as I have, you can then paint your moulding - a water based paint such as acrylic does the job well. Don't use oil or enamel paints, they tend not to dry on polymer clay (ever, I mean - it's a chemical reaction. I still have a sticky brooch from a dozen or more years ago, before I found that out). The painted moulding is at the right (click for a larger view).
There are several benefits to flexible moulds - the most obvious is that it's easy to get your item out of the mould! The most important plus point, however, is that you can have some small undercuts in your original item and still be able to stretch the mould enough to get the original, and your copies, out in one piece.
Disadvantages are that the moulds are quite easy to damage (cut or tear) if you are not careful with them, and if you press the clay in too hard without supporting the outside of the mould, you can end up with a very distorted result. On the other hand, that can make for an interesting piece!
The best way to support most moulds is to lie them flat onto your worksurface, then press the clay in ensuring that you don't deform the sides - if you do, push them back into place before turning the mould over and flexing to remove the copy.
Technique - Makling Flexible Mould for Flat-Back Items:
Two-part silicon moulding compound that is the texture of putty, and which can be mixed in your hand, is probably the easiest to use when making flexible moulds suitable for polymer clay. Check your suppliers for availability.
Take equal amounts of the two colours of the moulding compound (left), and mix them together by kneading until you have one single-colour piece (it will look marbled while you mix). I find it easiest to be sure I have the same amounts if I roll two balls, adding or removing bits until they look the same size.
Making sure you have enough mixed compound to cover your flat-baked original with a layer at least a quarter of an inch thick (to give support when the mould is in use), make a round, oval or otherwise suitably-shaped 'blob' and press your object into it (right). If you'd like the mould to have a flat back, put it on a plastic bag or similar on your worksurface. The compound does stick to paper when it's still soft, so don't put it on that! Leave for five minutes to set. Notice that in the feather-brooch that I'm using, the rubber has spread over the shaft.
When the mould is set, flex to remove the original object (right - click for a larger view). If there were parts of the moulding compound that went over the edge of your original, as with mine, take a pair of sharp scissors and trim off the excess.
Supporting the mould so that it doesn't distort, press kneaded polymer clay into the space, and flex to remove it. If you like, highlight the detail on the moulding with mica powder (such as Pearl-ex) before baking (before and after picture at right - click for a larger view).
Technique - Making Mould for 3D Item:
To use the same silicon compound to make a 3D mould, work it around the item. If the original has a flat or nearly flat base, such as a shell, leave that part uncovered, and when the mould has set you can simply flex the original out through the hole. If you find the hole isn't quite big enough, cut a line as below.
For an object that has no base, such as a bead, you can surround the whole thing with moulding compound (be careful not to trap any air between the compound and the object) and allow it to set. When it's ready, use a sharp craft knife to cut a slit, open up the mould and remove the original. You don't need to cut all the way around - half way is usually enough, and it leaves you with a mould that has a flexible 'hinge' so that the two sides are always aligned. If the shape is very complicated, you may need to cut more than one line.
This bead is small, less than half an inch, but the mould has still managed to make quite a good duplicate (see picture at the right). It's important to use the right amount of clay - I experimented by putting in a small amount, closing the mould firmly, seeing how much was filled, and repeating until I had the right amount. You can then either weigh the amount or just try to repeat it by eye. There will always be a little clay showing where the seam of the mould is - trim this off, and smooth it over with your finger before baking.
If I wanted to make a lot of beads, it would make sense to thread up a short string of the beads I wanted to use as the originals, and make a mould for the whole thing. Then I could mould several at once, and cut them apart before baking.
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