Please excuse my apparent ignorance. I am self taught via books and
this resource. I have been successful with most, but not all, of my
castings, and recently I am having a string of problems that brings
me to your sage advice. The problem at present, after much trial and
error, is porosity.
I mix the investment (Silcast20) at about 180 grams to 80 ml of
water. I follow the burnout schedule closely, with a thermo that I
believe to be reasonably accurate, however it is not digitally
controlled. I cast into a flask that has been soaking at 900 degrees
for at least an hour. I use a centrifuge, and oxy-acetalyne, and
sling the metal once it appears liquid and shiny, adding a pinch of
borax just prior. I get smooth, totally filled castings, except that
inevitably there are several pinhole pores on most every piece. I am
on a tight budget, and have been using primarily re-melted silver not
pure casting grain, some scrap some remelted trees.
Is it the old metal, a factor I have not yet controlled in my
Is it the flask temp, or am I overheating the silver?
Is the investment too heavy (it is nearly double the recommended
mix, however the packaging mix resulted in very fragile stuff that
tended to break in to the pieces).
Should I just go ahead and weld up a vacuum chamber for my pump?
Still, I feel foolish not mastering a tried and true method before
taking on another process…
Thanks folks, R.