Care during investment

How careful does one need to be around investment powder? Until the
1980’s there were no cautions. I am becoming active again, and don’t
want the vacuum table in the garage. I may prepare an area to mix in
and another to vacuum investment after mixed. I generally wear some
protection while breathing and mixing. I’d rather quit breathings
while mixing the powder, but have not succeeded very well at that

How careful does one need to be around investment powder? 

Careful. All dry forms contain crystalline silica in sizes capable
of causing silicosis. While it’s wet, ie being mixed after the water
is fully incorporated and no dry powder remains, or while a flask is
still setting up and moist prior to burnout, it’s not so risky. But
once burned out, it’s again dry, and in fact, perhaps the riskiest
part of handling investment is quenching or breaking out a cast
flask. The burnout process results in the silica crystals being
fresher/sharper than those in the dry mix, since mixing etc will
have worn down those particles a bit. Quenching releases, whether you
can see it or not, aerosol mists carrying the dry powder into the
air. Likewise, when you handle the dry powder to invest a flask, or
even when you’re sweeping up spills or cleaning the casting table of
dry residues, there are again risks of particles being airborne. Have
decent ventilation in any area where you use investment, and in most
cases, unless you’ve got really good, ie professional level,
ventilation, you should wear a decent respirator or at least a good
n95 dust mask. The respirators, since they seal much better to the
face, are much to be preferred.



I usually just read all the posts but don’t respond. This one I felt
the need to offer some input from my own experience.

I began casting in 1980, and usually used a cheap, paper mask when
mixing investment or breaking out flasks. It took about 22 years to
do so, but I have a moderate to severe case of silicosis which is
permanent, progressive and eventually fatal. Please install a good,
commercial grade dust collection system and wear an efficient mask
when working with the powder. I do now, seem to be very good at
learning the hard way.

Feel free to contact me off-list if you would like more

Jon Michael Fuja

Investment for gold and silver contains very fine silica which is not
good for you to say the least. You should be able to buy disposable
masks for use when mixing the powder and water, once wet I wouldnt
worry too much as the cured gypsum will bind the silica. Beware of
breathing the dead burnt investment when dry.

Nick Royall