I recently did my first (serious) one part silicone mold-making… I’m not counting that one time I made a bunch of severed Vincent van Gogh ears. I thought it might be helpful to share my experience and some lessons learned. Although this round of mold-making and resin casting wasn’t perfect, I’m really happy with the resin castings that I made and I’d call it a success!
Resin cast dreans.
The creature I was casting, which I ended up calling dreans, have these little antennas that curl backward. I found that either the cavity for the resin to go into didn’t form large enough or it otherwise had a hard time getting back into that little crevice. If the antennas were straighter (and possibly a bit larger), it might have saved me a fair amount of time in clean and up re-sculpting that area. I used Smooth-On Mold Star 15 Slow to create my silicone mold of this character and it’s nice to work with as it gives you a little under an hour to mix it and get it into your form. After that you want to give it several hours before you take it out of your mold form.
In the future I’m going to be better about having the right container for the job. I tried cobbling together a mold form with hot glue and scrap pieces of plastic, but that was a near catastrophe- I had to do some quick patch-work with hot glue to save the silicone from leaking out the side of the container! Recyclable plastic containers with matching, tight lids are your friend.
Watch Mold Making & Resin Casting of the Drean
There’s a whole method for calculating exactly how much liquid you need for mold making and resin casting… I didn’t do any of that. I sort of guesstimated and erred on the side of mixing too much. On the plus side, if you save your silicone scraps (or failed molds), you can actually use pieces or chop them up and add them to future molds so that you end-up using less silicone. In the interest of being more scientific (less wasteful), I did come across a method where you pour water into your mold, pour that out into a measuring cup and then mix your parts A and B mold material with a little extra as your still going to lose some of the material to being stuck to the insides of your measuring cups.
Another issue that I found was that I may want to use a resin with a slightly longer pot life- the two part resin I used, Smooth-On 65D had me scampering to pour it in the 2.5 minutes you have before it begins setting! I was casting characters that are smaller than a quarter, so I could imagine it being really challenging if you were casting something significantly larger. There’s a variant, Smooth-On 66D, that gives you 7 minutes to work with it and I think that would be a more ideal amount of time.
Pot life: refers to the amount of time you have to mix and pour a compound before it begins to undergo a chemical reaction.
While I had heard about degassing or vacuuming the air from mixed silicone, I don’t have a vacuum chamber. One thing that I could’ve done was do a long slow pour into the mold form. This is all in the service of preventing disastrous bubbles from forming on your mold, which would ruin it. Luckily I didn’t have any air bubble related mishaps this time around.
Using a dry brush to get baby powder into the crevices.
One of many things I picked-up from the Facebook group Shiflett Brothers' Sculpting Forum, was that baby powder makes a fairly decent release agent. I'm not sure if it’s good to use on pieces you’re going to want to put pigment in, but for things that you intend to paint or cast as white, baby powder works really well!
No matter how clean your casts come out, you’re still likely to need to do some clean-up to it. For this I used an x-acto knife and small files. I also had to fix those antennas that I mentioned, and for that I used a bit of Apoxie Sculpt.
Always handy to have some sort of markings on your mixing cups!
Another thing I found is that mold-making could end-up wasting a lot of plastic cups and other materials. After using more materials than I would have liked to, I did some research into creating less waste from it. If you can store the same cups that you're going to be pouring the same materials into, you can keep using the same containers. Any cup with some sort of markings will do, with a clear Solo cup likely being the most ideal or I’ve also heard of using soft silicone mixing cups, which I’m going to look into. You’ll just want to label them somehow and you can wipe-out any of the excess fluids by using a fresh paper towel for each surface- you’ll want to wear gloves for this. You can also reuse things like popsicle sticks as stirrers in such a way. It’s not perfect, but it’s better than creating a heap of single use plastics.
You also want to make sure you have nitrile gloves on hand, a well-ventilated work area, and you could set-up a fan at the end of your operation to circulate harmful vapors away from you. Wearing a face mask may also be advisable.
Well I think that wraps it up for just about everything I learned in this foray into mold making and resin casting. If you’ve got any tips to share, feel free to leave them in the comments. To be the first to know when I launch new polymer clay art videos, be sure to subscribe to my YouTube channel and hit the bell icon. Catch all of my videos here: https://www.youtube.com/thedreamsyndicatearts. You can also find many of the supplies I use in crafting here: https://www.thedreamsyndarts.com/supplies-gear/. And sign-up for my newsletter (in the sidebar) to get the latest studio goings-on! Thanks so much for joining me on this journey and until next time: Make. Believe!
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