I use vacuum and pressure to cast my snake blanks. I mix the resin and catalyst and put 16 ounces in a 2 qt jar, place it in the paint tank and turn on the vacuum pump for about 8 minutes. I then remove it, pour into the mold with the snake skins a pressureize the tank to abour 40 psi. I use 3 drops per ounce and leave it in the mold i=under pressure for about 4 hours and often I just leave it overtnight since I cast mostly in the evening. If you used more catalyst than I do, then 20 minutes and it could be into the jell stage whic means it jelled while is was vigorously bubbling under vacuum and will look the way you described. The amount of catalyst used is a function of how thick the casting is. Thicker = more heat = less catalyst. I've watched the resin bubble while under vacuum and it bubbles quite vigorously as the air escapaes. The size of the containter needs to be much larger than the volume of the resin.
Often excellent results can be had with using neither vacuum nor pressure, or just pressure, or just vacuum. Two of us experimented for almost a year with getting rid of bubbles and the process I explain in my snake skin tutorial is what we settled on. We reported our findings of what was working for us and the use of pressure tanks has exploded.
I'll bet HF has sold more in the last two years than they have in the last 10. My local HF only have 1 or two and now I see a stack of 8 or 10 on the shelf. What works in my shop may or may not work for someone else. Heck, it doesn't even work for me 100% of the time.
I'll say this before Curtis gets to: You won't have these problems if you use alumilite
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And I'll say that some experimenting should be done before expecting perfect results on the first try. Read all you can, ask others questions and ....I have two or three 5 gallon cans full of failures... But my success rate is much better than it was the way I was doing it.
From my experience, some things embedded in polyester resin tend to give more problems with bubbles than others. A coin has no air inside that can escape when the resin heats. Other stuff like snakeskin, cloth, and other porous material does. And the heat causes the air to expand and escape getting trapped between the embedded object and the jelled resin. This trapped air can present itself as bubbles or as a slivery lining covering the embedded object or as a crud covering the object and they all look terrible.
Do a good turn daily!
Don
Originally posted by sandking
<br />So I setup my HF pressure pot with both pressure and vacuum options.
I tried to put some clear resin from Michael's over a medallion I glued on the top of a bottle stopper. It was about 1/8" thick. After mixing and pouring on top of my stopper I placed it in the pot and pulled vacuum upto -20 for twenty minutes. When I released it it looked horrible. There were bubbles and spider webbing all over the place.
I also mixed some resin and did the same thing without putting it in the pot and it seemed to setup perfect without any bubbles.
Does this mean I wasted money on setting up the pressure pot????
