I did a casting project with the Iron Runt, to get her feet wet in the world of mini figure production. She sculpted a couple of very basic figures, and we took pictures of the mold making process. As promised, we're going to share that process with you all.
Now, this is a very basic rundown of how to do the most basic of mold making. There are a multitude of more advanced techniques, many that I am sure that I still need to learn. Sculpting and casting are a constant learning process, so please do not get discouraged if it doesn't turn out exactly how you want the first (or tenth) time you try it.
Here we have the Iron Runt, holding an Allumilite Starter Kit. The
kit retails at roughly $30, and includes everything you need to get
started, short of whatever you decide to make your mold box out of.
It has a small portion of silicone, just enough activator for that amount of silicone, modeling clay (more on that later), measuring cups, stirrers, and parts A and B of the casting resin. The silicone is hardly top-of-the-line, but for a beginner, it's perfect. Easy to mix, relatively easy to pour, and it's hard to be heartbroken if you mess up along the way.
Here are the "mold boxes".
One of them, I made our of Legos. I like this method, as Legos are reusable and removing the mold from the box is easy. I also like using Legos for the simple fact, that if you ever have to go back to add more to a mold (or in the case you wind up doing a two-part mold), you don't have to measure or guess the dimensions of the original mold box. It's very geometric, and easy to keep score of.
You can also use the modeling clay to seal the mold box on the outside edge, but for this exercise, I chose to seal it on the inside.
To the left, is the silicone provided by the kit. Any time you are working with chemicals, you want to make sure to protect yourself. Wear gloves whenever you're mixing any of the chemicals during
the processes of mold making and casting.
Now, I am mixing the activator into the silicone. There is exactly the amount of activator you need, included with the kit. It is important to not waste any, as it will throw off the mix of your silicone, which could compromise it's integrity.
It's very important to make sure that you mix the activator and the silicone base, very thoroughly.
When you pour into your mold, you want to hold the cup with the silicone well above the piece in the mold, and you want to angle your pour. A nice, thin stream will result and you can actually see air bubbles work themselves out of the silicone on their way across the lip of the cup.
You want to aim the stream of silicone at the piece, lightly covering the figure. Don't worry about filling the negative space around the figure: Gravity will do that for you. Concentrate on forcing that stream onto the figure in the mold. That will force air away from the figure, minimizing the amount of air pockets created. Air pockets will result in bubbles of product on your castings (typically in the finer details, exactly where you don't want them.) Once your mold is filled, you then want to take a solid tool, and tap the sides of the mold, to further promote the air bubbles in the silicone to rise to the surface. You can also vibrate the mold to achieve the same effect. This article is written based on the assumption that this is your first casting, and that you aren't investing in a vacuum chamber or pressure pot.
As you tap the mold, you'd witness air bubbles rising to the surface. You want to do this lightly, off-and-on, for about five or ten minutes (or until you stop seeing air bubble rise).
Once you are done with that step, you must engage in one of the hardest parts of the process: Waiting. Put the mold aside, and DO NOT mess with it for at least 24 hours. Read the instructions, and strictly adhere to whatever the cure-time specified is.
Once the mold has cured, and is completely firm to the touch, remove the mold box. If you used Legos, this is really easy. Just start taking the bricks off of the mold, piece by piece. Take the modeling clay off from the base, and let it sit for a couple of hours, to make sure that air can get to the inside of the mold.
From that point, you can start casting. There are as many casting techniques as there are mold making techniques, and that is another post for another day. But, if you follow the same basic principles (paying attention to the mix ratio, and pouring to avoid air pockets/build up), you should be okay. A lot of casting involves trial and error... Most pieces are pretty unique, and you should expect their casting experiences to be the same.
To summarize what I am trying to get at: getting started in mold making and casting, is nowhere near as scary as it may seem at first. You can get starter materials relatively cheap, and there are a multitude of resources online to help. Don't panic, and don't be intimidated. Mistakes will happen, you have to just roll with the punches, and learn from the experience.
If you have questions, leave them in the comments below.