Investing and Bubbles

Posted by Dan Caster on March 14, 1999 at 19:55:41:

I am taking a bronze casting class in Washington State at Olympic College.

The instructor likes using plaster and sand for investing rather than shell casting, and I like that way too ( of course I have never done any shell casting, so my opinion isn't worth much ).

I am getting lots of bubbles on the surface of the castings from small air bubbles trapped in the investment next to the wax. It is pretty discouraging to spend hours getting them off. What do you do to prevent this from happening? I read the discussions on the internet on wax and investing, but don't understand how to best prevent this. The instructor believes in spraying the wax with Sprayfixit to reduce the surface tension. There is no way to pull a vacuum on the investment at school to de-air it. I

could do something if I set up a foundry at home. No retarder is used with the plaster, either. There isn't any mechanical means to vibrate at school, but again I am reasonably good at kludging things if need be. Oh yes, some of the items are multiples in the same mold so it is difficult to apply the investment to the surface by hand. I think I would have saved a lot of rework time if I had applied some investment by hand to most of the surface and then did the sprueing.

Could you give me some tips on how to improve my investing to eliminate these casting defects? It wouldn't hurt to add these to the archives.

Cheers,

Dan Caster

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