I agree with Joe Lovato as well. I have seen the phenomenon of
investment getting sucked into a pore in the wax and leaving an
investment filled pocket in the final casting many times, especially
in large heavy pieces such as figurines and holloware fittings.
This can be remedied by careful inspection of each wax prior to
treeing and investing, particularly by holding each and every wax up
to a strong light, which will clearly show you any air pockets in the
wax pattern. Often these can easily be filled on a piece when they
occur in an area without detail. Otherwise, I just chuck it and make a
good one. Vacuuming your molten wax will also help cut down on these
Another misconception is that jagged, geometric shaped voids which
sometimes occur on the surface of some castings are the result of
broken off investment. These are most often caused by trapped air
bubbles in the wax which do not have a pinhole opening to the surface,
and burst under vacuum during investing. I have places waxes with
these defects under a vacuum and had the same result on the surface of
the wax, some burst, some don’t.
Checking each piece under a strong light and tossing those with
bubbles is the best way to minimize these types of defects. I have
almost never seen a defect I could attribute to broken off investment
in almost 15 years of casting, no matter how intricate the pattern.