Before we start this project let me warn you that it is a messy business. You should have some rubber gloves, a couple of tubes of clear silicone caulking compound, (don't get the odorless kind) some Xylene, (this is for cleanup so get a pint or so) a can of paste wax, a small bottle of glycerin, and some acrylic crafters paint.
You should be able to get glycerin at a pharmacy; you only need a little so get the smallest bottle you can.
Crafters acrylic paint is in any craft store; again you need to get the smallest bottle. Any color you like is good. The rest of the stuff should be at your local building supply.
If you have tried to use silicone for molds before you probably noticed that there are a couple of problems.
1 – It is a little thick and therefore difficult to spread evenly.
2 – It does not cure evenly
3 - It sticks to the Master like glue! I guess that is why it is sometimes used for glue?
I will show you how to overcome these problems in this little essay.
The first thing you do is get the Master ready. He would like a nice coat of that paste wax. Put it all over him and smooth and buff him until the surface is nice and shiny. I told you this was a lot of work!
Take as much silicone as you think you will need to cover your Master and put it in a plastic bowl. The bowl should be big enough to allow you to stir the silicone.
A tube of silicone is about 10 ounces so you can get a rough idea of how much you have in the bowl by estimating how much you have taken from the tube. For each ounce of silicone add 5 drops of glycerin and a drop of paint. Mix these together and add them to the silicone. Go easy with this and only use minimal amounts. The more you use the weaker the silicone gets. Stir this until you have a uniform color. That is why you added the paint, without it it's is hard to tell if you have the glycerin completely mixed. You are using clear silicone so you can see if you have any air bubbles trapped in your first coat. You don't want any, so try to get it mixed as smooth and even as you can. Don't stir any more than you have to, stirring can create air bubbles.
You now have between 15 and 45 minutes to spread this over your Master. I use a soft plastic spatula about 1 inch wide. This seems a bit small bit it makes it easy to keep the silicone coating even. Make the first coat thin, about 1/8". It is the most important coat. This is the one that holds the details. The working time depends on temperature and humidity. If it is hot and warm you have 15 minutes! In a cool, dry place you will have 45 minutes or more. You may want to try spreading this on some throw away masters before you try to do your first "real" mold. You have to get a good, even coat on the first time. I can't stress this enough. If the first coat is no good you may as well start over.
It should be cured in about 3 hours. I wait a couple of hours before I start with my 2nd, 3rd, etc coats. These can be thicker and you don't need to worry about any air pockets. I don't mean that you can have huge air holes in the silicone, but small ones are not a major concern. You will want to build up to at least ¾ or more inches of thickness. Be sure to fill any undercuts on the outside of your rubber mold.
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