THE Process+ added how I made the double sided charms

Start with a hand drawn sketch and scan it into illustrator. Trace/draw/simplify the image in illustrator.


The illustrator file is then uploaded to the laser cutter.


Cut the model from plastic. The quickest way to do this seems to be to etch/print the detail first and then separately go round the outline of the image with the 0.01mm line to cut it out.

Using the cut out plastic models you can make your silicone mould. You will need to measure the size of your model and make a wooden mould to hold the silicone. Place buttons in the corners, these will work as reference points.


You need to make a channel for the pewter to flow into the mould. You can do this by shaping some plasticine/blue tack.

Cover the base and the buttons in graphite to make it easier to remove the silicone later. Do not put graphite on the plastic model as it will affect the surface finish.

Attach the side of the wooden mould with duct tape.


Make sure there are no gaps you do not want the silicone leaking out.



Once the mould is ready you can start to mix the silicone.
I have worked out that I require 200ml of silicone to fill the first half of the three moulds.

The pot of silicone may need a bit of mixing before pouring into a measuring jug as the contents may have separated slightly. Measure out 200ml of silicone. If there is a number of bubbles on the surface of the silicone it is a good idea to remove these. To do this you would usually put it in a vacuum to extract the trapped air. As I do not have vacuum apparatus available I am using an old broken saw to vibrate the bubbles out.


Once the bubbles have been effectively removed you can add the hardening agent. A label on the pot of silicone will give you the correct volume to drops ratio, eg 200ml approx 36 drops.

Mix the hardening agent in well but taking care not to get air trapped that could cause bubbles. This will need vibrated/shaken up to get any air out.

Once you feel that the solution is as bubble free as possible you can start to pour it on to the moulds. Start in one of the corners and take your time, move around the outside of the plastic piece. The silicone will gradually move itself to take up the space available. Fill all three moulds making sure everything is covered and all the silicone is used up.

During pour air will have gotten trapped in the mould and it is very important to make sure these are removed or the mould will not work. So take time to vibrate/shake each of the moulds.



Once you are satisfied that the bubbles have been removed leave the moulds to set. The suggested time for setting is 5 1/2 hours. Personally I would leave it over night, giving it 8+ hours to set. That way you won't be tempted to open your mould up too soon and ruin it after putting all the preparation and time into it (silicone is not cheap either, I estimate it is costing me £5-10 per mould).

The mould should be completely set when the material is hard but has spring in it. It should not be tacky. You can now remove the silicone from the wooden mould. You may need to tidy up parts of the mould with a craft knife. To do the make part of the mould you need to cover it with graphite.



You can now start to re-build the wooden mould, but this time place the plastic model side upwards.



Mix the next batch of silicone. This time you can use a bit less, just enough to make a even layer on top of the first half. I will be using roughly 150ml is total. Once again check the pot for the details on volumes etc. Use the same process as before- making sure there are no bubbles when you move on to each stage and make sure you leave enough time for the mould to set.

You will now have to two halves of your mould and you are almost ready to start casting.
Switch on the hob/heating element and place a metal container with a small amount of pewter in side to heat up.



You may need to tidy up your mould, put in a channel for the air to escape and cover it all in graphite.


Put the two halves together and place a piece of mdf on either side to support the mould for when you put the clamps on.



Check the pewter to see if it has all melted. You can use a thermometer to check the temperature (max temp 310 degrees). Basically if all the metal is melted and the viscosity looks good for pouring, try it. Remember it is extremely hot so gloves and a mask are advised, and lift the container with pliers.


Don't worry if it over flows, it is better to pour to much than too little. Also whilst pouring it is good to tap the container to help the metal flow through the mould and to encourage the air out. The pewter will only take a few seconds to solidify but it will still be hot to the touch, so it is a good idea to leave the moulds so the pewter can cool for a couple of minutes.

There is a certain amount of trial and error in the first few casts. You may need to widen the pouring or the air channel or even add extra areas for the air to be pushed out to.

This image shows that the cast is incomplete and shows the extra holes for the air. This piece of pewter can be melted down and reused.

 
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Since I last update this I developed my moulds so that the charms were all double sided. I did this simply by inverting the original illustrator sketch and cutting it out into perspex. The rest of the process does not change, except for when you make the second half of the silicone mould. Instead of replacing the original model in with the flat side facing up, you put the inverted model in, so that the rigs (cut outs) face upward and can be cast the silicone.