Freitag, 8. August 2008

Resin Casting step-by-step

over the last few weeks several people have asked me about resin casting and a tutorial or walk through. Well, as we all know, casting is a sensitive topic as it is very easy to violate copyrights and intellectual properties. But I think if you do your own models and pieces and don't copy others property, then casting is a very helpful asset.

That said, I also want to say, that I am in no way the best caster, or the best knowledge base around :-)
To me, the best casting tutorial around is that of Ultramar:
It is extensive and very clearly written and well illustrated. His tutorial is what I used to learn.
*bow before Ultramar*

Please also note, that I link to the Rai-Ro modeling shop, because I buy my products there. I have no relationship to them, nor am I paid for this in any way :)

OK, without further ado, here's what I use:

(from left to right)
  • A flexible plastic bucket for mixing the components
  • (in front of it) a small mixing bowl with gradations for measuring
  • modelling clay
  • Modeling bricks (like Lego) to build the form for the mold
  • 1:1 Silicone (a sample product can be found here:
  • The Model :-) Yes, there it is a modified Kinder egg capsule
  • Mold separating agent (spray can)

So at first, I spray the model with the separating agent. This will help to later remove the model from the mold. There are different products for this, one is to be painted on the model, but I prefer the spray agent, as it is a lot more evenly distributed (and thinner on the model).
Usually, the model must dry a few minutes before it can be used in the molding process.

Next, I start to build the mold.
For this I use the modeling bricks (like these here: to build the form that takes the silicone.

To ensure it is leak-proof and none of the precious silicone can flow out of the form, I use some modeling clay to seal it at the bottom.

Once the form is built and sealed, the model can be placed in the form.
Please note that you may have to build a small pedestal, so the model itself doesn't touch the ground (and the underside of the model can be covered by the silicone).

Now I mix the silicone - this here is a 1:1 mix silicone, so that is very user friendly!
It is pourable for about 10 minutes and dries rather quickly in between 30 and 60 minutes.

Once the first half of the mold is created and dry, the top of the silicone must be prepared by some silicone separating cream. This is necessary, so that the two halves of the mold won't stick together.
Please be careful to apply this paste. If you don't cover all the silicone, the two pieces stick together and may ruin the whole mold, however, if you put it on the model, it may leave some cream on it, which will then be visible in the actual cast.

Then I mix the next batch of silicone and complete the upper half.

Please note the two squares and notches at the bottom end of the mold. These make it easier to later fit the two halves together, when casting.

Now, a word about the model itself.
When you build a model with the intention to cast it later on, please make sure that the model or piece of it, does not contain any "loops" under which the silicone may flow, or you will probably have to do some cutting, to get it out of the mold.
As you can see here in the red circles, I did have such loops, from the tank connectors, and I had a hard time to get it out of the mold.

Also on the hatch, I had a looping spot, and the plastic broke off, when I removed it from the mold.

Any protruding piece of the model can break off, when removing it from the mold - despite the separating agent.

OK, so now I have the mold ready for casting.
I decided that I will cast the top piece (with the hatch and motor) first, and then use it like a cask cover on the second half of the cast.

Since I never know how much resin I will really need (mathematical n00b that I am) most of the time there is some excess. It is always good to have some small items/molds near by to receive any excess resin so it will not be wasted.
Here I have the mold for a walker foot, and a winged skull emblem ready to receive any excess.

This is the resin I use for casting ( ). This is also a 1:1 mix, and very thin.
It makes excellent casts, and I am very pleased when I work with it - despite of its rather high price.

So here I've poured the resin - and filled the other molds with the excess.

The clear resin becomes opaque and white as it cures.

Once the bottom half is completely dry, I mix the second half of the resin and fill it in the lower mold.
Then I place the upper mold like a cask cover - this way melting the two halves into one.

Here is the walkers foot that I cast:

And the winged skull emblem:

After about 2-3 hours I carefully separated the first half of the mold. As anticipiated, the motor area that had the loop (red circle) will need some cleanup, and in the right exhaust pipe there was an air bubble (small red circle), so I will have to fix this later with some putty or pipe.

But all in all, I'm very satisfied with the result.

Completely free from the mold, there is still some cleanup to do.

... to be continued.