Have I gotten bad batches of Alumilite Clear (Slow)? I’ve been using this resin for months now and all of a sudden I’m getting these defects. I’m using the same silicone mold and I vacuum the resin before I pour. It looks like some of the same star shaped defects shown in the bubbles thread (see below).
After reading that thread I thought maybe my half full containers got contaminated somehow because they were only a month old. I ordered some new product ($160.00) and tried again. The photo shows the results with this new batch of resin.
Are you using any release in the rubber mold? As I posted recently to another topic, sometimes this shows up in a brand new mold where you may have some uncured aspects of the tin silicone still laying around.
Also, how big is the part? Are these stars all over or more so on one side or another?
That is strange that they just started recently. Is that corner one of the bigger or thicker areas ... it almost looks like it is trying to pull away from the mold as if it were shrinking. The thicker areas would have a tendency to do that more than a thin area but still doesn't explain why they've just recently started.
Couple more questions ... Do you preheat or warm your mold prior to casting it? Have you tried wiping or cleaning the mold out before casting? Do you have any mold release ... Stoner or UMR there? How many parts have you pulled out of that mold you are using? ... and does the surface feel any different?
Often when you pull parts from a silicone mold over and over ... eventually the mold will dry out and the surface will feel a little drier or more crusty. Just wondering if you are noticing anything different about the mold?
Sorry for the 20 questions ... just trying to figure out what is going on? Mike
The mold is basically new. We've molded about 30 pieces. I don't use mold release because I don't want anything that could diminish the part surface. I keep the mold very clean and, like my other molds, I store them so no dust/dirt/contamination can happen.
My latest test reduced the number of bubbles and eliminated the star affect. Instead of pouring directly into the mold I placed a wood popsicle stick in the corner and used it as a pouring ramp. That seemed to almost fix the problem. I'm down to 5-10 small bubbles. I pour slowly to prevent bubble forming around some inner details.
I have but don't usually heat the mold. It's a relatively thick part so I'm not concerned with curing issue. I also move the mold to a cure oven (@150/16hrs) after the resin has solidified.