Latex rubber moulds have been around a very long time. Traditionally, they are used for Plaster of Paris or stone-craft moulding, but they work equally as well with wax to make some very unusual novelty candles. On better quality moulds, the detailing can be quite superb, and the flexibility of the rubber means the candle can be removed without loosing vulnerable pieces - something you just couldn't achieve with polycarbonate or metal moulds.
The very fact that you can achieve some superb figures with rubber moulds can also be a double edged sword. The shape isn't uniform, which can make wicking them for burning a bit of a headache. A lot of novelty candles are sold for their beauty alone, and never really meant to be burned, but you should state this on the packaging.
Using Rubber/Latex Moulds
Before you use your rubber mould for the first time, it's a good idea to turn it inside out and wash it with a solution of washing-up liquid and water. Allow the mould to dry naturally. This leaves a very fine film of lubricant on the mould which helps with releasing later.
Rubber moulds don't have a wick-hole manufactured into the design. That would be a bit of a disaster for stone craft moulding and the moulds are designed predominantly for that use. You'll need to decide whether or not you want to dedicate your mould to candle making, or if you might want to use it for traditional moulding at a later date.
If you decide to dedicate it to candle making, you have the choice of creating a wick hole or not. Creating a wick hole allows you to wick your candle before you pour, as with any other candle mould, which is probably better for larger candles. for smaller candles, you might like to leave the mould intact and insert the wick once the candle is out of the mould, by using a hot skewer or needle and creating a wick channel down the entire length of the candle. The wick is then inserted using a wick needle, into the channel you've just created.
Your mould is going to need to be supported as the wax hardens. The moulds have a 'base' or 'plinth' built in to the design to give you a large area to support the weight. This is the area you will need to build your support for. A brilliant, cheap way of creating a support is to use a thick cardboard box. Double-walled boxes are ideal, and you usually have one or two knocking around your home. The box need to be lager than your mould, to allow it to be suspended without squashing any of the parts. For most moulds, you can simply cut a circular hole into the cardboard box, with a diameter less than 'plinth'. It needs a good supporting rim so that the weight of the wax doesn't pull the whole thing through the hole you've created. Once you're happy with your set-up you're good to go! Wick your mould if that's the method you have chosen, but make sure the wick hole is well sealed.
Pop your mould into your support unit and melt your wax. REMEMBER - do not add stearin as a release agent! Stearin will perish you rubber mould. Use VYBAR instead. Vybar can be added at the rate of between 2-5%. It will give rigidity to your paraffin wax, gives a lovely opacity and vibrancy to colour and help release the candle from the mould.
Once your wax has reached pouring temperature, put it into a pre-warmed jug and start to pour it into your mould. I find it useful to pour in stages. Pour a little into the mould to make sure you don't have any leaks from the wick hole. Tap the mould gently between each pour to make sure any air bubbles have risen to the surface and every little nook and cranny has been filled. Repeat the process until the entire mould is filled. Keep the surplus wax for topping up.
Suspending the mould in a box allows good air movement around the setting wax, so it cools at an even rate. There will probably be shrinkage as the wax cools, so keep an eye on it and top up as required.
Once the wax is firm, you can release the candle from the mould. The easiest way of doing this is to rub the outside of the mould with a washing-up liquid/ water solution to give it some lubrication, then gently roll the mould back on itself, taking extra care with ay bits that protrude, you don't want to wreck your candle by knocking them off.
Once released form the mould, the candle can be wicked with a needle if you haven't pre-wicked it. allow the candle to rest overnight to fully harden and then paint, bronze or decorate any way you like to bring the detail to life!