Silicone Mold Making from Form 1 Parts - Silicone Cure Inhibition

I’ve been working on a silicone mold, using a part I printed in MakerJuice Form1-compatible resin. I’ve had some real issues with cure-inhibition on the surface of the part. I’m spraying 2 coats of shellac on the part, before the mold release brfore pouring the Silicone. I’m using a platimum-catalyzed silicone rubber, so it’s a known problem with some chemicals preventing proper curing.

Has anyone made molds off parts printed in FormLabs resin (preferably with platinum-silicone). Are you coating the parts first? Are you doing a special UV cure? I’d appreciate any insights you might have.


Andy Hudson

Anne has been making some pretty killer molds. Might be good to ask your question here:


I’ve had success (no inhibition) with casting platinum-catalyzed silicone directly in molds made from Formlabs clear resin that were only coated with mold release.

However, I’ve also found that some types of platinum-catalyzed silicone (e.g. formulations for encapsulating electronics) are more sensitive than others (e.g. those used for creating theatrical props).

Cure accelerator additives might help in cases where you are seeing inhibition, but using them may start to get bit pricey. (From my understanding, they basically contain additional suspended platinum catalyst.)

I’m printing a mold in formlabs gray resin for a silicone part (smooth-on dragonskin, shore A10, fast set time) as I type. I’ll let you all know of the results.

I had to get a printer replacement, so this took a bit longer than anticipated, but it appears the grey resin works perfectly for molding platinum cure type silicone. In fact, no release agent is needed at all. I would say that the grey material, at least as I have not tried other colors yet, is a perfect material for this application. What a relief! Cheers to the chemists @Formlabs1!

I haven’t had a problem casting in Platsil 20 Platinum Cure on Black or any other. I do leave them to dry outdoors for at least a day before casting though. Im a professional prop maker and use the same grades of silicone on all of my work from specialist fibreglass/casting companies.

We have been having issues with creating molds using a battery of Smooth-on silicones. Presently we had some cure inhibition issues with Dragonskin 30A. We were able to demold but now kinda stuck. I have 10 Fast in the mold (I cleaned it with IPA and baked at 65C for 15mins to get rid of the extra juice. ANybody have similar issues? Maybe we are not mixing correctly.

Your molds are not fully and completely cured (IMHO). I’ve needed to keep mine outside in direct Sun for a day to make it work well. I’m building a post-print curing lightbox now, and I’ll post a howto/parts list when I’m done.

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I have been making silicone and organic rubber molds from plastic printed parts for a couple of years now and there are some things to watch out for.

  1. Make sure your part is clean, no lacqueres or varinishes on them because they may react and possibly bind or inhibit the cure of the silicone.
  2. I have used a mold cleaner to quickly clean any residue off a part, this is a cleaner also used as a rubber cement thinner. It has an extremely low flashpoint so take care and use adequate ventilation. It dries nearly instantly and doesn’t seem to effect plastic parts from 3d printers.
  3. Lightly spray the part with a mold release. I have extremely good succes with Price Dricscoll’s Ultra 4 Urathane Parafilm. This is a paintable mold release and really helps. Just a very light quick spray does the trick and it is dry.
  4. Big thing with silicone rubbers is try to buy just what you need and use it within 6 months. Buy from a reliable supplier that has a good stock turnover or you may get expired or nearly expired rubber that will may not cure or cure inconsistently.
  5. There are different types of silicone that can be used. RTV (room temperature vulcanizing) that most need a vacuum chamber to take the bubbles out, Smooth-On sells an RTV that doesn’t require degassing but pouring is critical.
    LTV (low temperature vulcanizing) that are in sheet form and can be formed around the model but require a vulcanizer and a temperatures just under 200°F and can be purchased through Romanoff International or Contenti. Lastly one of the easiest to use is the 2 part putty version sold by Smooth-On and Contenti that you simply press around your model at cures at room temperature. With the putty type it is best to have some sort of mold frame that you can press the putty in and try to eliminate any voids. With dry forming silicones you should use a light dusting of mica powder between your mold sections and over the part (mica powder will not work with liquid silicones).

I have been making molds from prints since before the dawn of the Form1. I have never had an issue with any silicones from this website:

They also sell Price Driscoll’s Ultra 4 Urathane Parafilm.

They seem a little pricey, 2part putty at $45 lb and Contenti is $29.44 at 1.2lbs, Smooth-On has 2lb kits at $39.71

When i was starting I thought Aeromarine had more size options and is easier to find the right product. Buying too much is bad for me because it often expires, making it technically more expensive. But if you know what you want and they have your size Smooth-on is great.

I used Smooth-On for a project where I was doing a cold cast emblem (resin filled with brass powder) and they were the only ones I knew that carried those materials. Really nice company to deal with and I found the trial size to be more than enough material for the job.

Majority of my purchasing goes through Romanoff and some through Contenti, both outstanding companies to deal with and very helpful. I happen to use them because the supplies they have work specifically with the equipment I have.

My ideal size is a half gallon. It runs out about on the expiration date.