The technique for making flat backed objects such as badges, pendants, wall plaques and other jewellery items is generally the same. The silicone resin jewellery moulds can be made by either pouring or brushing the silicone onto the original piece. Pouring is probably the easiest method for all items with a flat back. The process is as follows:
Select a suitable container
The first thing we need to consider for this method is how to contain the poured silicone when we pour it over the original model.
With smaller items we are lucky to have a large range of suitable containers which can be easily obtained. Ice cream containers, takeaway food containers or even butter containers are just to name a few. We are looking for a container which is about 1-2cm bigger than the model all around the sides. We need the container to also be 5cm taller than the model.
If your item is extremely small you may not even need a container. You can fix the small model to a small board with a non hardening clay or glue if you prefer and build up a wall around the model with clay or even lego bricks.
With larger items instead of fixing the model to a board you can fix it directly to the base of the container you choose. It is important to fix the model securely to the base so that it will not float to the top when silicone is poured in.
In this article we will go into detail the method which uses a food container.
Using a plastic food container as a mould dam
- The first thing you need to do is to secure the lid tightly onto the container. Turn the container upside down and cut the bottom out of it.
- Now secure the model to the base (which will be the lid) of the container with glue or clay.
- The application of release agent is not usually needed when using silicone as it sticks to very few items. Glass is one item which silicone tends to stick to. It is a good idea to do a small test if you are unsure. If you find a release agent is needed you can make your own with petroleum jelly dissolved in a solvent such as white spirit. We use a ratio of 10% petroleum jelly. You can then spray or brush the solution onto the model and let it dry. The white spirit will evaporate leaving a fine even film of petroleum jelly behind on the model.
- The silicone we use to pour over the model comes in two parts and needs to be mixed together to start the curing process. The mixing ratios depend on the silicone you use and can be found on the label of your silicone. We find waxed disposable paper cups to be ideal as mixing containers and wooden stirrers or paddle pop sticks for mixing.
- Pour part A and part B into a new container and mix thoroughly scraping the sides and the bottom of the cup to ensure proper mixing. Make sure you do not whip air into the mixture as this will create excessive air bubbles. A folding action is best.
- Once it is mixed pour the mixture into a new mixing container. This ensures that no unmixed material remains in the cup when pouring it onto the model.
- If there are areas on the model which have very fine detail or undercuts it is advisable to brush some silicone onto those parts before pouring. This will ensure that the silicone will flow onto each and every surface and minimize the chance of air bubbles on these high detailed areas.
- You can now start pouring the silicone onto the model. Pour in a thin stream from a high point over the model. This thin stream from a high point will force any bubbles in the mixture to pop on the way down. Also start pouring onto the lowest point in the mould container. It is best not to pour directly onto the model so aim for the floor of the mould container. Continue pouring until you have 1 cm of silicone above the highest point of the model.
- Leave the silicone to set overnight. You can de-mould the model the following day by removing the lid from the container and pressing the silicone gently from the top. It should slide out the bottom. The model should easily pop out from the silicone and leave a cavity ready for casting. Let the silicone mould cure properly for an additional few days for longer mould life.