Beginner casting, which crucible size is best?


I am a novice jeweler. I bought a used casting machine that is
originally for dental casting. The crucibles he gave me were really
small and possibly contaminated. The crucibles slide into place with
a d slot with their bases being rectangular. The slot part is
removable for different sizes of crucibles… I need new crucibles
(preferably large and deep) and the slots to match. Where would I
order these things and how do I pick the sizes to fit the slots I
already have if I can’t order new ones? I need good tongs too for
smaller flasks! How do I know which is best? I have a small tank the
man gave me and he said acetylene or propane works for melting
silver…Do you think so? Where would I get it filled for acetylene?
Also I need some boots for my flasks-preferably the kind with a bump
in the middle with the hole you fill with wax…(for smoother
silver flow). I’ve always used larger equipment at a school so I’m
getting really frustrated!

Thank you for any
H. J

Hi Hannah,

The dental casting machines tend to be pretty limited in terms of
the size of crucible and flask they can handle. Rings,
(one-per-flask) are probably about all you’ll have the room for. If
you’re lucky, he had a jewelry machine, and just used small flasks,
but the odds of that are low. How big is it? Does the flask end pivot
with an elbow joint? (So that the flask end swings to about 90
degrees relative to the angle of the main arm.) If it has an elbow,
you may have a jewelry sized machine. (may, just may) If it’s solid,
it’s probably a dedicated dental machine, and rings are pretty much

Crucibles may be an issue. I’d call one of the larger suppliers, and
see if they can help you. Pictures emailed to whomever you end up
talking to will probably be key.

As far as the gas bottle goes, it’s either acetylene or propane. You
can’t switch. Acetylene tanks are sort of skinny and built like,
well, tanks. Propane tanks look like (and often are) BBQ grill tanks.
(in the US, they’re often white.) Take the tank to the local
industrial gas supplier (in phonebook under “welding supplies”), and
they can tell you what the tank is, and what you can do with it.

Hope this helps,

I am a novice jeweler. I bought a used casting machine that is
originally for dental casting. 

H.J. If you have a brand name… do a search for it and see if you
can find the mfg. If not… Rio Grande carries several different
crucibles and the rubber sprue bases. If you can find a crucible
that is close, you can modify it A LITTLE with a Mizzy wheel…
You’ll be white when finished so use ventilation…best done
outdoors if possible…makes a heck of a mess. I had an OLD Lucas
caster for many years and always had to modify new crucibles.

In 35 years of casting, I have never found a sprue base that makes
the metal flow like I want it to. Right after removing the base from
the flask, I always take a thin spatula I have had forever and I
taper that indentation to suit myself. Starting at the cavity hole,
I like a little area with 90 degree walls… about 3 to 4 mm
high… about the size of a dime or nickle in diameter, (depending
on the flask size) then I make the sides smooth and to look like a
funnel out to the bottom of the flask. This lets a nice button seal
off the flask…the 90 degree area gives some depth to the button.
This maintains heat in the button, keeping it molten just a little
longer…allowing the casting to “drink” as it cools. This stops a
lot of porosity and gives a better all around casting.

I suggest only Acetylene for melting silver… I always had problems
trying Propane. Make sure the tank is in date and safe along with
the hose & torch. Its… “Just your life” ;-).

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