Mould making: Problems with silicone

The first half of the mould did not harden as expected. I put a little too much hardener in the silicone and didn't have time to mix it properly, so some parts of that piece remain sticky even after a couple of days.

The surface is supposed to be firm and definitely not sticky like in the picture below (that's a closeup of my finger and the surface of the silicone that did not harden).


The problem with that batch was that it was so small, only 50 g. It is easier to measure the hardener for a larger amount of silicone, so I used 100 g for the next try and made several mould halves at once. This time everything went as it should.


I also decided to make one mould for a wedge sole. This one will have a very large opening and the reason for that will come out later as I explain the casting process.


The pink dots you can see on the surface of the silicone in the picture of the three mould halves are drops of the form separating agent. I don't know why it did not spread more evenly like it did when I used it for the models. Anyway, that was the next problem.

I managed to get the right amount of hardener in the next batch of silicone for the other halves of the moulds, so that went fine. When the silicone had hardened and it was time to separate the mould halves, things didn't go as expected. The halves were stuck together. I had to use a hobby knife to cut the moulds open. Fortunately, that worked fine and now I have moulds for the soles.


I have already cast a couple of soles with the moulds, but I will go into that in the next post as there are still things that need to be figured out.

For the Finnish post, see here.

Mould making: Silicone

The master from the previous posting is not finished yet, but I made another one from polymer clay and wood. I wanted to see how it would work and it turned out fine. I didn't paint this one, but varnished it with water-based varnish (solvent-based varnishes do not work on polymer clay).


After varnishing, the master needs to be treated with form separating agent, which is basically liquid wax. It will help to get the master out of the mould at the end of the process.

For the mould, I'm using Silcolan NV mould silicone. It is white and fairly thick, but it should settle well even around small objects with many details, so it should be fine. The biggest problem is the amount of hardener. Add too much and the silicone will start to harden before you're finished pouring it, add too little and the mould won't harden (or it will take very long).


After the master was treated with form separating agent and silicone and hardener mixed, it was time to press the master into the silicone. Now I just need to wait for the silicone to harden.


The next stage will be applying form separating agent over the entire surface, letting it dry and then pouring in the silicone for the other half of the mould. The form separating agent will keep the two halves separate.

Finnish post is here.