New Mold + Clear Resin = Yellow?

suwalski · Post by **suwalski** » Wed Sep 29, 2010 10:36 am

Hi guys,

I have a question that maybe one of you more experienced folks can help answer.

I recently finished new molds for my parts (used Alumilite QuickSet). The molds turned out really well, and the opaque SmoothOn comes out really nicely.

However, when I used my water-clear Alumilite, I got a goopy, yellow mess. The next time I was more careful, and it was less goopy, but still very yellow. The third time around I decided that maybe I'm just having really bad luck with this fresh batch of resin, and I cast in the new and the old mold from the same mix:

http://pat.suwalski.net/temp/refit1000/ ... yellow.jpg

The new one's on the left, and it turned out less yellow and firmer than the previous castings, but the old mold still produced a significantly clearer and harder casting.

Is this normal for clear resins to need a broken-in mold? Is there some logical explanation to all this?

Thanks guys.

modelnutz · Post by **modelnutz** » Wed Sep 29, 2010 12:49 pm

Good chance you're dealing with alcohol leaching from the new molds.
Try baking the molds in an oven at 180 deg. for an hour....let them cool and apply a good coating of mold release.

Ziz · Post by **Ziz** » Wed Sep 29, 2010 2:30 pm

Or just cast some more regular parts from the molds to naturally leech out the alcohol, then try a few clears.

suwalski · Post by **suwalski** » Wed Sep 29, 2010 3:13 pm

Thanks for the advice. I actually did bake them at 175 for about an hour before that last casting and that helped a little. I always use Stoner.

I noticed that the colour of the rubber is starting to fade in places. I assume this means it's stabilizing. I guess when the fresh rubber smell goes away I'll know it's ready.

I guess I'll start building up the opaque inventory, then. Thanks, guys.

USS Atlantis · Post by **USS Atlantis** » Wed Sep 29, 2010 6:12 pm

Ya, if you're still smelling 'fresh rubber" it's still leeching

If I'm doing clear parts, I'll do a 2-3 hour bake of the mold at 150 before any casting

Umi_Ryuzuki · Post by **Umi_Ryuzuki** » Wed Sep 29, 2010 6:31 pm

I leave my molds to set for seven days, minimum before casting clear resin.

suwalski · Post by **suwalski** » Wed Sep 29, 2010 7:48 pm

All excellent advice. I'm surprised they don't list this in any of the FAQs out there. Thanks a bunch, guys.