Thursday, October 24, 2013

The Process of Custom Design: Part III. Casting.


This the third entry in a four-part series on the process of custom designing a piece of jewelery.

Now that the wax model or CAD representation has been accepted by the customer, it is time for casting.

Casting is a process by which a liquid material is poured into a mold (or a flask) that contains a hollow cavity of a desired shape, and then is allowed to solidify. Casting is a 6000 year old process. The oldest surviving casting is a copper frog from 3200 BC. For more information see Wikipedia.

The most common method of casting is by lost wax. First a channel called a sprue is attached to the wax model.  It is also made of wax. On more complicated pieces, multiple sprues of varying diameters are used. Next the model is place upside-down inside a flask and a heat resistant plaster is poured all around the piece -- encasing every minute detail. A vacuum is used to make sure all the bubbles are removed. After the plaster sets, it is put into a kiln and heated in a controlled manner to melt out the wax. Thus the term lost wax casting: a perfect negative of the piece is made and the wax destroyed.

Custom pieces when they come out of the flask.  Notice the sprues.

After proper heating in a kiln to remove the wax, the flask is ready to be filled with a precious metal. After the metal cools down and hardens, the flask is submerged in water to loosen the plaster and out comes the piece, sprues and all.

In addition to lost wax, there are several other casting methods.  Here are a couple:

Vacuum casting is used with silver and gold alloys only. A vacuum is created under a flask and molten metal is poured into the opening. The vacuum helps the metal flow into all the spaces.

Centrifical casting is used with most metals including platinum. This can be quite exciting to watch because a special machine is used to shoot the molten metal into a flask at very high velocities to ensure a complete casting.

Tony, our custom jeweler, demonstrating centrifical casting.

The final step is to cut off the sprues and finish the piece. Finishing is the subject for the fourth and final part of this series.

Wednesday, October 9, 2013

The Process of Custom Design: Part IV. Finishing.

This the fourth and final entry in a four-part series on the process of custom designing a piece of jewelery.

Once the sprues are cut away, the resulting rough areas on the custom piece are filed flush to the surface of the metal. If the piece is a ring, then Tony will clean the inside with a sanding drum and check for correct size.  The entire piece is inspected for defects.

Testing a ring just back from casting to make sure the stone will fit correctly.  Notice the rough edge on the shank where the sprue was cut away.

The ring when it has been finished.


Next it is methodically cleaned.  This step is also the process of getting the surface to the point where it is ready for polishing and includes sanding.  Any concave areas are sanded with a mandrel, while convex areas are sanded with a sanding stick. In sanding (as well as filing and polishing), there is a progression from using coarser tools to finer tools. A rubber wheel impregnated with an abrasive is used on delicate areas. Pieces with hard-to-reach areas are placed in a magnetic tumbler.

Now it is time for polishing. Jewelers will always bring a custom piece to a high polish stage in the finishing process, even if it will eventually have a matte finish. When polishing Tony uses buffing compounds, again from coarse to fine, and a variety of other buffing materials such as muslin, felt, and bristle. He will continue polishing until a mirror finish is achieved.

Sometimes when pieces come back from casting, they need to be assembled. There are two major techniques to joining metal: soldering and laser welding. Soldering is a must with two different colors or types of metal. If joining pieces of the same metal together, laser welding can be used.  Solder employs using the same carat metal but alloyed differently to result in a lower melting point than the parent metal. Solder is usually designated hard, medium, and easy. These designations refer to the melting point and are particularly important in complex pieces that require several solders. Tony will always work from hard to medium to easy.  This prevents any previously soldered joints from melting apart. In laser welding, the same metal is used to join parts together. For example, 14k yellow gold laser wire would be used to weld 14k yellow gold parts together.

This yellow gold pendant has two components.

The finished pendant after the pieces were laser-welded together.


Once again it is time for ultrasonic cleaning and a high pressure steam to remove all traces of polishing compound. If there are no stones to set, the piece is finished.

If there are stones to be set, the first step is to prepare a seat.  A seat is a ledge or a shelf upon which the stone rests. Metal is folded over the stone to hold it place. This is a rough way of describing setting.  There are at least twelve different techniques for setting stones but in each the jeweler must create a seat and then "fold metal over the stone."

A mounting ready for stones.

See how the metal is folded over to keep the stones in place?


After the stones are set, the piece is polished and cleaned again. Any engraving that was specified is completed and -- viola -- a beautiful custom-made piece of jewelery unlike anything belonging to anyone else anywhere.

This concludes our series on custom design.  We hope you've enjoyed learning about the process!