I created a mold and cast several pieces using Alumilite White, and they look great. Then I cast some using RC-3 Black, and the surface has a horrible, mottled appearance, completely unusable. I've used this same Black resin before and sometimes get a good casting and sometimes they look like this, and I've never been able to figure out why. One thing I've noticed is that the "B" part of the resin seems to develop a grainy sediment over time (we're talking just a couple of months or so, not years). At first I thought it was that sediment causing the problem, so I tried drawing it from the top without shaking it, but got the same results. Any suggestions?
In the attached photo, you can clearly see what's wrong with the black one. It's hard to tell with the white one, but it's perfectly smooth, exactly what I wanted.
A couple of things here..... Is there any chance that moisture could have got in to the "B" side ...an example would be the cap left off in a humid environment.....I get sediment too sometimes, I just chalk it up to moisture (humidity) that gets introduced to the jug over time.
I always vigorously shake the "B" side for 2 to 3 minutes before doing anything with it.
I pour Alumilites AlumiRes RC-3 so the fallowing comes from my notes on this.....
Mix between 25 and 30 seconds ...I use a stop watch as every second counts from mixing to pouring.
I have aprox 3 minutes of work time......that's from the second I stop stirring to when the resin is getting too thick to flow correctly......this is where I think you are getting into trouble.
I usually get sediment in the B side toward the last 1" to 1/2" left in the bottle of tan RC-3. But it usually doesn't mottle up like that though it will show dark spots here and there without changing the surface. A good shaking before mixing like Brian said usually helps mine but if you can, you might could salvage that one with sanding.