AZGem Gems
December, 2002
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.

 

Jewelry Casting

This month's subject, jewelry casting, is the logical follow-up to last month's story on wax carving, or jewelry model making.

Because the two subjects are closely related, there will necessarily be some repeating of things mentioned last month.

While there are several ways to make a piece of jewelry, we'll discuss a typical process for casting a piece in 14 karat gold.

The process is called "lost wax casting."

Pictured here is a model of a ring done in wax. The wax becomes "lost" when it's melted later in the process.

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 post.

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 (before finishing)
  • 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...

  • Crucible 
  • Flask
  • Sprue base
  • Tongs
  • 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 together.

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 crucible!

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 crumble.

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 set 

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Jewelry Dealers

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 business.

The holidays are behind us for now, but there's Valentine's Day, Mother's Day, birthdays, anniversaries, and other special days just ahead.

There's always a market when you're selling jewelry.

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Gem Special Offers

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.

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Thank you

We look forward to 2003 with excitement.

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.

Carolyn Doyle

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The Dorado Company
P.O. Box 8232
Scottsdale, AZ 85252-8232