Making your own Silicon Moulds

I recently went on a Resin Jewellery-Making Course that also included an introduction to making your own silicon moulds. It was a fascinating process that I thought I would share with you because, whether you are making jewellery or other items such as soaps, you can produce unique items rather than things that everyone else can buy a mould for.

First step is to find or make the things that you want to create a mould of. I gathered a bunch of nature-inspired jewellery pieces including brooches, pendants and charms that I would love to be able to make copies of. But as luck would have it, almost everything I chose was not suitable because either they were not solid (e.g. openwork dragonfly wings) so the silicon would just ooze right through or because they would be too fine and delicate for the resin to flow easily into in the finished mould (things like gecko toes or insect legs). I ended up with one item I had brought with me that would be suitable – a scarab beetle. I borrowed a starfish charm and a seashell from my classmates and a couple of larger, chunkier pieces from the tutor.

In this course we were focusing on items that had a flat side and learned how to achieve this even if the bottom wasn’t absolutely flat. It is important that you make sure that no silicon can ooze underneath your object (although you can cut it off later so it is not critical but it is better to do as much preparation as you can upfront to avoid having to do remedial work at the end). For objects that are flat you can simply stick them down using a glue-stick (go right to the edges). If your object is uneven you can use an oil/wax based modelling clay such as Claymate: roll out a thin stick of the clay and shape it around the edges of the bottom of the object; press it down firmly onto the surface and use a blade to cut away any excess that has bulged out the sides.

To make the silicon moulds we stuck our chosen pieces onto glossy cardboard (recycled packaging). You can fit more than one object into a single mould but need to fit them closely together (about 0.5 cm apart). Next step is to cut strips of the cardboard long enough to fit around your objects, taping pieces together as necessary. You need to make sure you have a tight fit around the objects (again about 0.5cm) and can bend the cardboard to the appropriate shape. Once you have the cardboard in about the right shape, you apply a hot glue gun to the bottom edges (just a few dots all round) and then press the cardboard surround into place and let dry. Then most important of all, you need to apply a thick layer of hot glue around the outside of the join and make sure that it is completely sealed – silicon will ooze out of any hole given half a chance.

Another learning moment was to choose objects of similar height if you are combining them in a mould. I had one flat item and one egg-shaped one so it would have required a lot of unnecessary excess silicon to cover both together. A last minute repair gave me two separate moulds that could be filled to the appropriate heights without wastage.

Before we pour in the silicon the final step is to make sure that you have thoroughly cleaned your objects with methylated spirits on a rag to remove any dust, fingerprints, hairs etc as these will be beautifully moulded into your objects every single time. Of course you can use this to your advantage if you are wanting to create a piece that has texture. If you have used the modelling clay to create the object you are making a mould of, then you will get whatever markings are on the surface of the clay. You will not get a smooth finish on your finished piece unless you have a completely smooth finish on the object you are making the mould from.

We used a two-part Translucent Silicone Rubber for which you mix Part A and Part B in equal amounts, making sure that you transfer all of Part A into Part B (scraping down the sides well) and then mixing very thoroughly (bottom and sides as well) to make sure it is completely combined. If you don’t stir well enough then you risk having parts of your mould that don’t set properly. Although not desirable, it is still okay as long as it is not a critical part of the mould. Make sure your mould template is on a flat surface and then start to slowly pour the silicon in – staying in one place and pouring from high enough up that it forms a thin string going in (to reduce bubbles forming). Keep pouring slowly and allow the silicon to settle itself into all the crevices. Don’t be tempted to pour all over the top or to use an implement to force the silicon into spaces. If bubbles do form, the best way to deal with them is to pick up the whole thing and drop it firmly (not too hard) onto the surface.

It doesn’t matter if you don’t have enough silicon to start with, you can easily mix up some more and pour it on top whether it has set or not. It will not leave lines or layers. Once you have covered your objects by about 0.5cm then you leave them to set – using a heat lamp can speed the process up. Touch gently to make sure the surface is fully set and very firm before you attempt to release your mould.

Then you are all set to start moulding. Use methylated spirits rather than water to clean your moulds and spray lightly with methylated spirits to keep them flexible if you are not using them for a while.