The World's Most Useful
Gem & Jewelry Monthly Newsletter
Written by Carolyn Doyle for customers of
The Dorado Company
and other visitors to the azgem.com website who subscribe.
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Usable Gems... and a little opinion.
This month's subject, jewelry
casting, is the logical follow-up to last month's story on wax carving, or jewelry model
Because the two subjects are closely
related, there will necessarily be some repeating of things mentioned last
While there are several ways to make a piece of
jewelry, we'll discuss a typical process for casting a piece in 14 karat
The process is called "lost wax
Pictured here is a model of a ring
done in wax. The wax becomes "lost" when it's melted later in the
This picture also appeared in last
month's story. A reader wants to know... "is the hole in the middle of the
ring for a gem?"
The answer is no... but almost. The
hole is for a peg head which holds a gem. A peg head has prongs above and a post
below. Picture it as looking something like a stud earring with a short, fat
O.K., on with jewelry casting!
As with other arts, jewelry casting has its own terms, specialized tools, and materials.
Jewelry Casting Terms
- Casting - The process of injecting molten gold or other
metal into a cavity
- Casting - the rough gold jewelry piece
- Casting Grain - Gold alloyed
with other metals, depending on the color and karat purity desired,
made into small pieces
- Investment - A non-flammable plaster of
paris-like material that
makes a fine grained slurry when mixed with water
- Sprue - A wax tube that creates the path
the molten metal will follow
- Wax - The model medium, and sometimes
the finished model
Jewelry Caster's Tools
The photo shows the basic tools used to cast a
piece of jewelry in gold.
The pieces (from left to right are...
- Sprue base
- Casting machine
- Flask cradle
- Crucible carriage
Click on the photo to visit Alpha Supply Co'
website and see more tools and descriptions.
The basic machine is a centrifuge,
a machine that slings (or, uses centrifugal force) to move molten gold from the
crucible into the void left in the investment.
The flask is a tapered metal sleeve which
holds the wax model and investment.
The sprue base does double
duty. The wax sprue is attached to the wax model on one end and to the rubber sprue
base on the other end. The sprue base then covers one end of the flask.
The crucible is a clay or other high
temperature tolerant vessel in which metal can be melted with a torch.
Lost Wax Casting Process
The first step is to weigh
the wax model with wax sprue wire attached. By means of a formula, the
amount of gold required to cast the piece will be calculated.
Next the wax model is mounted
to the sprue base so that it stands up from the base. (Note the cone shape
in the center of the base. This is called the sprue button.)
Then the flask is placed over the model and
base in a way that the base seals the bottom opening of the flask.
Investment is mixed to a slurry consistency
and slowly poured into the flask, completely covering the wax model and
taking care to minimize creating bubbles.
The investment is then subjected to a vacuum
process or gentle vibration to eliminate any tiny bubbles.
The investment is then allowed to set up
until it is hard. At this point the rubber sprue base is removed revealing
a funnel shape created by the sprue button.
This funnel shape will eventually guide
molten gold into the mold.
The flask is heated in a kiln for several
hours at increasingly high temperatures to vaporize and eliminate the wax.
Now in the center of the heat resistant
investment there is a void in the exact shape of the wax model.
At this point everything starts to come
The hot flask is removed from the kiln and
placed in the casting machine.
The crucible is placed in the machine next.
Now the proper amount of gold casting
grains are melted using a torch. Casting grain is used rather than scrap
gold to assure a quality casting.
Casting grain is properly alloyed to meet Federal
Trade Commission regulations.
Casting grain is also formulated with
traces of other substances to help the gold flow and prevent creation of
voids (bubbles in the cast piece).
When the gold reaches the proper
temperature the spring loaded mechanism is released, the centrifuge arm
swings in an arc with great force... and the molten gold is forced from
The molten gold is hurtled through the
funnel shaped opening in the investment, along the path created by
the sprue wire, and into every nook (and cranny) of the mold.
After the cast flask cools a bit, it is
plunged into a bucket of water. This causes the investment material to
Now the steel flask and the casting can be
removed from the water.
Next the gold sprue is cut off and the
casting is inspected for quality.
Assuming all those critical steps that we just
talked about went well, the carved wax model has been transformed into a
beautiful gold ring.
The ring is then polished and gems
We hope all you new dealers are having
success and enjoying yourselves. Isn't the jewelry business fun and easy!
For those thinking of becoming a dealer, now is a
great time to join the program and jump start your new jewelry
The holidays are behind us for now, but there's
Valentine's Day, Mother's Day, birthdays, anniversaries, and other special days
There's always a market when you're selling
Check out the new traffic
building feature we're experimenting with. You can buy featured gems at
or below our cost.
All you dealers... these featured gems are a great buy. You can increase your
profits even more with these gems.
We look forward to 2003 with
Several of you have taken advantage of
our gem special offers and gotten a really good deal!
The jewelry dealer program is helping
us expand our core business... wholesale gems and jewelry, and it's
enjoyable. Working with enthusiastic people is always enjoyable.
Thank you for a successful year.
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The Dorado Company
P.O. Box 8232
Scottsdale, AZ 85252-8232