Moldmaking Silicone for casting very tiny doll parts?

Does anyone have experience with this and have any advice?

I'm close to making master molds for my tiny fairy, about 13cm realistic proportions so everything is super tiny and thin, and the joint slots are also very small. I've made tons of junk one piece molds to remake parts and finish them up using some cheap translucent silicone off amazon but find it's quite soft (I believe it's 15-16 shore A hardness), doesn't return to it's shape repeatedly well, leaving large seams, and the thin parts for slots tear and break easily after just a couple pours.

I would like to stick to one part molds for most of the pieces to avoid seams with such tiny hard to sand parts, so was originally thinking of using sorta clear 37 or 40 but thought maybe that would be way too firm for one piece molds, even with cuts down the sides. I'd also like to use a clear silicone to help with keeping cuts clean and ensuring the small vacancies are properly filled with resin, which I have had trouble with, even using a pressure chamber. There is sorta clear 18 which I'm leaning toward trying at this point. But if there's something better and more durable for tiny parts I would use solid colour silicone. Also must have extremely little shrinkage.

Anyways just wondering if anyone has home cast their tiny dolls and what works best for them. I'd be so grateful for your knowledge!

 

Thank you rianif I did manage to cast just a few dolls with the supplies bought last year but I gave two of them away to family for Christmas and am keeping the last two from this first attempt. I need to update the project page with all the info but have been procrastinating a bit since the fairy is not technically done and ready yet. Soon!

But yes I really wish someone who had experience with casting their tiny dolls had been willing to help, I asked several places but the advice I was given from other artists wasn't specific enough to tiny dolls. I even emailed the silicone company for clarification on their products but got no reply! I'll update here now for anyone in the future who may benefit from this info because I believe in sharing knowledge, especially when it comes to costly supplies that can make or break an artist.

In the end after much research I settled on a trial size sorta clear 37 and dragon skin 20, and tried three different resins, smooth cast 305, 326, and task 3.

For making one piece cut block molds you absolutely want a firm silicone, 20 is not enough, and for filling those tiny joints and thin spaces you NEED as transparent as possible because even under 60 pound pressure the bubbles won't fill in without some manual help, so I would never use anything other than sorta clear 37 or 40 ever again for tinies. The cuts do need to be long so you can fully open the molds but strength isn't an issue as the silicone doesn't tear. The dragon skin was a bust as it was too soft and quite fragile, despite the technical data indicating good strength qualities. The dragon skin sticks like glue to the smooth on resins after a couple uses, flakes and tears off with the resin and makes a huge mess, I wish I'd just gotten two sorta clears instead. Dragon skin is also very opaque so useless for seeing where resin settles.

For resin, 305 works the best for this use. It is thin enough to fill the molds, cures hard in the allotted time, and reacts well to pigment and UV additive.
I'll have more to say on the other resins in depth later in my project thread but suffice it to say the 326 takes a Long time to cure fully, days, and adding color/UV lengthens the cure time even more. Task 3 was another waste as it's super viscous and unable to fill the tiny sprue holes fast enough before it cures. Degassing causes issues as it doesn't return to the mold after the vacuum. It also sticks horribly to the dragon skin and is brittle. It does have a nice glowy effect like "french" resin though, I managed to get one doll cast from it and she's very pretty. But it's also very slick compared to the 305 and her joints don't pose quite as well.

So I had to make part of my molds out of dragon skin as the trial size of sorta clear wasn't enough, even for a tiny doll, and as a result I need to redo at least some of my molds due to damage. I also want to modify the joints a tiny bit for better posing, so may as well just redo all the molds. As such I need to buy more silicone, and resin as the 305 ran out, and unfortunately just haven't been able to afford it yet.

 

Yes those are shore A hardness. Thanks for sharing these tips Lillith, I appreciate it! I also marked my pieces, but used a sharpie and didn't do the best job of it, I've learned from that and will make better seams next time. Also maybe used the wrong type of pen as it left some ink on the mold after which was annoying, what do you use to mark your parts?

I studied Harucasting's molding photos for help and am grateful he shared this method online because it was very useful.

Shore 30 or so would have been my preferred hardness but unfortunately the sorta clear only comes in 37-40, otherwise I likely just would have gotten that. Having a little bit of experiece now I would agree harder is better for two part molds.

 

Sharpie is a permanent marker but for some reason it left ink on the silicone. I used Mr surfacer. In any case I'll try something else next time. The overhead pen is a good tip, though I'd prefer to steer clear of messing with the mold in any way after cutting as a fresh cut makes a great seal and almost no seam lines. A bit of water may not affect the stickiness though. Harucasting seems to use Gundam markers, maybe I'll try that.

 

Yes, I don't see how a tool like that could be utilized for silicone molds, the mold needs to be flexible to allow undercuts to be removed. Although technically I do inject the resin into my molds under some amount of pressure, using syringes. The issue is viscosity of resin and tiny cavities of .5mm or less makes it hard to avoid air pockets and bubbles. Which is why clear silicone is important.

 

@MisticUnicorn This information is fantastic, thank you so much for your thorough review of this silicone, it indeed sounds really great and I'd like to try it out!! Especially the no shrinkage thing, it's something I've had to grapple with as I cast and recast parts several times while refining joints. The smooth on platinum silicone is pretty good but it still seems to shrink a little bit. That library life is amazing too It actually sounds perfect for prototyping as you said, really curious what the cost is for the liter kit, it doesn't show without an account.

Thanks again for taking the time to share your experience and recc for this unusual silicone, it's so helpful and appreciated