Let us say that one wants to burn out a flask and does not have
a kiln. What are the alternatives. Can you use a gas grill, a
hot plate, etc., etc.?? Please advise.
You can use all of the above and a few other things. Here's a
method that's gotten me thru a couple of emergencies. You need:
1) an electric hot plate *without* a thermostat (it must be "on"
at all times); the nichrome element type is recommended, not the
calrod type. 2) a terra-cotta flower pot big enough to cover the
flask, allowing about an inch of extra space both vertically and
horizontally; 3) a sheet of heavy-duty aluminum foil big enough
to wrap the inside of the flower pot; 4) a well-ventilated area
with a power supply for the hotplate, and 5) at least 6 hours of
your time for an average 2 x 3-inch flask with, say, a single
gent's ring wax or an average ladies' ring or two.
Place the flask on the edge of the hotplate with the
sprue-former end downward. Situate it so the molten wax does not
directly contact an element when it liquefies and flows out.
(It's best to place a little aluminum foil below the flask
opening to catch the bulk of the wax -- wax that sticks to the
hotplate can be removed with denatured alcohol or nail polish
Turn the hotplate on a low setting and leave it uncovered until
most of the wax has been eliminated. Every couple of minutes
lift the flask with tongs and observe to see if the wax is
flowing freely, not boiling out. Adjust temperature if
necessary. This process should take 30 minutes or so on average,
but don't rush the process!
When little or no wax is flowing out, gently increase the
temperature setting and move the flask incrementally toward the
center of the hotplate with your tongs. If the wax starts
sputtering and splattering you're going too fast and can ruin the
mold. Reduce heat and go back to Go. Allow up to 90 minutes or
more to complete moving the flask to the center of the hotplate,
increasing the temperature to the highest level as you go.
When the flask is at the center of the hotplate, cover it with
the inverted flower pot to create a mini-oven. Burn-out from
this point should require about 4 hours (more for larger flasks,
The advantage of using an electric hotplate instead of an open
flame or barbecue briquets (it's been done!) is that the
investmen is not carbonized by the flame, so it's easy to judge
when all the wax has been burned out. All traces of gray will be
gone and the investment will be a uniform chalk-white. It's
usually best to cast immediately after removing the flask from
the heat, but this is a very imprecise process and experience is
the best teacher. Practice with commercial waxes first, and
don't start with your priceless originals!
Warning: do *not* use sections of galvanized pipe for flasks.
When heated they can give off poisonous fumes. The best source
of cheap flasks I've found is my friendly neighborhood muffler
shop. They have a bin of cut-offs they let me pick through. I
have them do all my muffler work, of course, and send all my