[Colin]

I’ve been using polyester resin for a few weeks to make polyhedral dice sets, and recently made a new set of molds using sprta-clear transparent silicone. Initially, I made a single test mold, which went great, the resin cast great. Same with a second test one, however after making the last 5, the resin has come out of the molds with wavy veiny lines, akin to shrink wrapping, even from the molds that initially came out great. Holding them up to the light, the affected sides looked like they has a tiny gap between the resin and the mold, instead of pressed right up to it. At first I thought it was an issue with the molds, as they showed the imperfections, however after cleaning they were back to smooth. I’m using correct proportion hardener, mixing thoroughly, everything is dry, and doing everything the same as before. what could be the issue? The only thing I could think is temperature, as it used to be 19°c and past few days has been 17°, though with just 2 degrees affted it so much?

[Katherine Swift]

Hi Colin,

It sounds like you are experiencing excess heat and shrinkage with your castings. Have you tried mixing a batch with less hardener?

[Colin]

Hi Katherine, thanks for the reply.

I think it’s something about the molds, past few casts I’ve been using some of the older molds as well, with the same resin mix, those turn out fine but the new molds dont. The old silicon was a pink mix, the new one is transparent. After casting the clear molds I did cut out some for a pouring channel, could that have affected it at all? The chamber itself wasnt touched but maybe the overall density did? That might explain why the first 2 clear molds worked very well but then didnt after cutting. I did try using 1% hardener instead of 2%, that came out exactly the same.

[Author]

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