Mould Making with RTV Silicone

In this multi-part article, Stuart Nicholson from tabletop-terrain.com shows us how to make a mold like the one in the picture to the right using RTV Silicone, or Room Temperature Vulcanising Silicone to give it its full title.
This tutorial focusses on 'garage' one sided mold making with off-the-shelf RTV silicone and casting with resin/plaster products. Using one-sided molds you can replicate spectacular terrain and modelling details to improve your gaming table.
Two sided molding is possible with these techniques but I find the results are often disappointing. For high-detail two sided molding you really need professional and expensive pressure vulcanisers and spin casters.
I learned mold making simply through Googling the web and trial and error. Hopefully this tutorial will save you some expensive mistakes and be at least as useful as others already out there.

Tools & Materials

The RTV product I use is called 'Ultrasil' manufactured by Barnes, an Australian company, and available from TopMark in Auckland who are excellent to deal with if you happen to be a New Zealand mold maker.
Ultrasil is a 1:10 RTV (room temperature vulcanising) product consisting of a large pot of white rubber and a small bottle of blue hardener. I strongly recommend purchasing RTV products with coloured parts like this, because having a coloured hardener makes it very easy to see that your silicone is fully and uniformly mixed prior to pouring.
You should be able to find similar products wherever you live and while it's beyond the scope of this article to attempt to list them all, I recommend that those in the US should check out Hirst Arts site mold making page and/or related forums for US product suggestions. In fact you should probably check out their site wherever you live because there's a lot of mold making information on there plus myriad examples of ways in which it's useful.
Other things that I'll be using in the course of this tutorial include a small previously set mold, a cheap hog bristle brush, a permanent marker, a clean pot to mix in, a mixing tool (cleverly disguised as an HB pencil) and a large 1L bottle of beach sand. I'll explain what they are all for as we progress.

A Few Words About Masters

The first step to creating a mold is having something you want to copy in plaster or resin. You should expend a considerable amount of time creating your masters because any errors and or blemishes here will be reproduced on every piece you cast from your mold. Sort them out NOW.
You should aim to make your masters as sturdy and as highly detailed as you can. Make them sturdy because it's always nice to keep your masters after molding them for future modification and possible remolding. Molds created with most RTV products do not have an infinite life so being able to create additional molds from your master can definitely be useful. Particularly if you're a hobbyist seller like myself. In fact the pieces I'm molding here have already been remolded several times.
Make them highly detailed because once you have successfully created a mold you can easily reproduce them, producing tens or hundreds of casts with ease (and a little time). So it's worth applying all your modelling skills and equipment in the creation of a master worthy of molding.
Finally I'd like to point out, and I know you've heard this before, that copyright applies to all original works and apart from being illegal to breach it, it's just not fair to the original artists. Surely we as terrain makers should appreciate and respect the efforts of our fellow artists?
There may be an occasion when you want to replicate that souvenir pencil sharpener that your Aunt brought back from her trip to Egypt so you can use half a dozen of them to decorate your mummy's tomb terrain piece; and nobody is going to make a big fuss over that. However it you want to start selling them on eBay then out of respect for your fellow artists you owe it to them not to steal their work and should sculpt one of your own.
Take it from me: it's infinitely more satisfying to reproduce your own work anyway.
In the next part of this article we will begin the process of creating a mold.