Andrew Lubow on sat 28 mar 98
I started out in crafts as a silversmith and still find casting a great use
when I need a one of a kind element for a design. If you approach casting
with common sense you'll find no extreme hazard to it.
One of the books I keep in my library is Tim McCreight's, The Complete
Metalsmith, Davis Publications, ISBN: 0-87192-240-1. It's a extremely
complete, well illustrated and easily comprehendible. One technique in it
uses is a handle attached to a jar lid with wet newspaper in the lid of the
jar. This creates steam when held down to the hot mold. Pressure from the
expanding steam forces the molten metal (in the sprue) into the mold. I've
done this and find it extremely simple to do. Read the book. It gives more
detail you'll need to understand.
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From: John H. Rodgers
To: Multiple recipients of list CLAYART
Date: Friday, March 27, 1998 7:25 AM
Subject: More on Unusual Customer Request
-- [ From: John H. Rodgers * EMC.Ver #2.5.02 ] --
Just wanted to follow up on this a little, because there are some serious
safety issues involved.
When working with the noble metals, you are going to be working with liquids
at temperatures around 1500 to 1700 degrees F. You DON'T want any mistakes.
The issue of blowback is a serious one. If you get spattered with liwuid
metal at those temperatures you are going to experience serious burns.....
tissure damage beyond repair.
Casting these days is done in closed protected containers to ensure that any
blowback, leak or what have you will not result in injury.
Although casting can be done simply by pouring molten metal from a crucible
into a mold it does exposed you to the explosion/blowback danger.
Typically, molds used for lost wax metal casting of gold or silver are made
from investment plaster, and are baked at high temperature (around 1350F) to
remove any residual wax, or entrained moisture. Then using either
centrifugal or vacumn casting the melted metal is injected into the mold. It
is immediately cooled below solidus, then plunged into cold water which
causes an explosion of steam under water which breaks up the mold, freeing
the casting inside.
A borax compound is added to the liquid metal and it is stirred with a
carbon rod at times. The action of these two items is the removal of oxides
and impurities from the metal just before casting. Ideally the mold
temperature should be near the molten metal temperature to avoid thermal
shock and eliminate porosity in the casting. The oixide removal before
casting also helps.
Cuttlebone from the cuttle fish can be used to make a mold to cast gold or
silver into, but the same principles apply, except the heating of the mold.
Be extremely cautious when working with the hot metal. Wear longsleeve
clothes, gloves and safety face gear.
-------- REPLY, Original message follows --------
Date: Thursday, 26-Mar-98 07:49 AM
From: John Baymore \ CompuServe: (JBaymore)
To: Clayart \ Internet: (email@example.com)
Subject: Unusual Customer Request
Of course, the WORST CASE is that you would break the mold, so be sure that
you have it in a separate container so that you could catch any overflow.
The gold can always be remelted & used again.
Actually, pouring metal is a skill that has many variables, like clayworking
.. From my very limited experiences working in the foundry when I was
employed at Massart, one thought comes up that might be more of what would
be like a "worst case":
If the fired mold has any slight water content in it (not preheated over 212
for a long time), that water changes to steam instantly and can blow molten
metal all over the place. Nasty if you are in the way. Seen it happen
doing investment work with bronze.
Also if you are doing lost wax (or "lost styrofoam", or other dirty-type
burnout techniques) and the vent sprues plug up, the gases produced (nasty
stuff too) as the hot metal hits the wax can blow the molten stuff back out
the pour hole.
Do some research first or find someone who knows pouring metal. Small
foundries are located all over.
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
-------- REPLY, End of original message --------