Friday, 7 October 2016

My top tips for casting toys and figures in resin and rubber. Saving on materials, preventing bubbles.

After 4 - 5 years of making primarily hand cast toys, I'm finally collaborating with the man who taught me how to pressure cast, Austin aka Gold Dober. I'm very honoured and personally very happy about it.
I've collaborate now with everyone (except for COTU world) who I looked at in the beginning and wanted to have a go at resin production myself. I'll update with details when I have them.

This isn't going to be a guide on how to cast for complete beginners, more a few things I've come up with along the way to help me with troublesome molds, and to save materials.


You probably know what a waste mold is - it's where you make a mold using waste silicone. Any silicone that isn't covered in mold release will bond with whatever curing silicone is next to it. Think of it like hardcore and concrete. Hardcore is cut up pieces of old mold, concrete is the new stuff which bonds it all together. You will need a pressure pot for this to work though.


All of my large molds are made with a lot of waste silicone.
Here you can see the blue chunks that were used from previous molds and the pink from new silicone. They are different shores, brands, etc, but it all sticks.


I did a quick vid on instagram how to replace part of a mold that is mostly fine:

As long as the original model is strapped in tight, the mold should be perfect. The rest of the mold will still give way eventually but these weak spots can be fixed several times. Here are the results of the above video, you can see the shapes that will make the negative shoulder articulation- ive already had perfect pulls from it:


By that I mean, "topping up" molds where you haven't poured enough, or having bubbles because you didn't cut fat enough ducts make the sacrifice of a bit too much resin worth it.

With really bad undercuts, like the back of Blade's hat, I use a method of letting it leak. You can see that I've sculpted him so everything except the hook (which can be vented easily as it's near the feet) is facing upwards, meaning I could in theory have just one vent from the hook to the leg, and one from the feet to the bottom and I'd be fine.
But the back of the hat is facing the opposite direction. Casting in rubber, I wouldn't havea  hope of that being bubble free...

So I drill a hole from the outside to the back of the hat's peak. The material leaks a tiny bit, but also takes all the bubbles with it. 

 Here's something you can do with fast curing stuff - stick a toothpick or stick all the way through...
 Leave it in and pour the material (resin or whatevs) at the top.

Pull out the stick - it creates a vacuum, rushing material to the hole on the side.


I learned with plaster before I used resin or silicone, and then i tried casting without a pressure pot or vacuum. I learned some stuff that still comes in handy.

1: Air can't go where something solid is.

I sculpted this giraffe head (Im putting this custom in store BTW) with horns at the top, they are narrow with bulbous tips, meaning theres an area that needs resin with a small amount of space for the resin to get though. Also, down  at the bottom of the mold, air will get trapped there first. 

 So again, I put a stick there. It holds that narrow part open and also blocks anything (air or resin) from getting there.
Pour in the resin with the stick still in the mold.
Pull it out and dispose, as there is no air there to go to that part, all that can get in is resin. Obv works better with a pressure pot but helps still if you're not).

2: Poke, bang, and rock.

If you're casting something really thick, or are casting without a pressure pot, you can minimse bubbles in a few ways. You can poke the areas where bubbles happen before the resin cures, with a stick, you can bang the mold from several angles to try and smack out the bubbles, and you can pour a little resin in, and rock the mold. With only a little resin, rocking should make a shell inside the mold wihtout enough liquid to trap air (bubbles). Once that's at least half-cured, you can pour in the rest. Any bubbles will be internal, where you can't see em!


I try to always have a mold at hand with a wide opening that I can pour into quickly. All my leftover resin after a pour goes in these, and after a few pours, I end up with some bonus casts.

Also, I've recently expanded my Bigcartel store (upgraded account) and am putting in EVERYTHING I have in the studio. I'm really low on space so it's all priced to fly.

No comments:

Post a Comment