For Your Staff:Selling Quality
Cast Jewelry: A Primer
Knowing how cast jewelry is made demonstrates another aspect of quality
in your shop
by Mark B. Mann
Director of Professional Certification
Jewelers of America
Lost-wax investment casting was formally established in the early 1900s
in the dental industry and was embraced enthusiastically because it ensured
great accuracy in creating reproductions. It soon evolved into a process
for jewelry, where it has grown to be the largest manufacturing category.
The casting process that has resulted from nearly 100 years of developing
technology is not so scientific that it's fail-safe. In the hands of those
unprepared to meet its technical challenges, casting has the potential for
To make sure you have the know-how to avoid these pitfalls, we'll focus
the next two installments of the Quality Assurance Guide on these important
aspects of casting:
- Methods and observations for identifying cast articles of jewelry (in
- Quality features of cast articles of jewelry (in this issue).
- Identification and analysis of common defects resulting from improper
casting (written by Tom Weishaar and appearing in the June issue).
Overview of the Casting Process
The goal of lost-wax investment casting is to create wax copies that allow
mass production of articles basically identical to a handmade original.
For anyone unfamiliar with the process, here's a much-simplified explanation:
- Begin with a piece of metal jewelry called the model.
- Make a rubber mold by covering the metal model with a solid mass of
layered, unvulcanized rubber and subject it to heat and pressure to vulcanize
or "cure" the rubber.
- Using a surgeon's knife, dissect the rubber mass and remove the original
model. Unless the rubber mold is removed carefully, the lines where it's
cut called parting lines may show on the resulting wax model
- Inject molten wax into the rubber mold; the resulting wax reproduction
is used as the master to produce mass numbers of the article.
- Place the wax model in a flask, surround with investment (a plaster-like
compound that withstands high heat).
- After the investment has set, the assembly is placed in an oven to
create the mold for the jewelry.
Identifying Marks of Cast Jewelry
Irregular, Free-Flowing Design
Both these rings are cast. The free-flowing design of the ring at left makes
its cast origin fairly obvious. That origin isn't as easy to detect in the
other ring, which has a symmetrical design that easily could have been hand-fabricated.
Lack of Precision at Wire Junctions or
The illustration at the top shows wires fabricated together. The detail
is not "joined," rather it's crisp and precise. The illustration
at the bottom shows the identical junction of wires, but it is rounded and
"joined" typical of cast reproductions.
Unfinished Areas Are Unpolished and Have
Slightly Granular Surfaces
Cast jewelry often has hard-to-reach areas that because of time
and labor are impossible or impractical to polish and finish properly.
Unless the rubber mold isdissected very carefully when the wax model
is made, the result may be a seam or parting line on the wax that is never
removed by the wax finishing department. This defect is transferred to the
final piece and sometimes not removed by the metal finishing department.
Cast items are only nearly as good as the original model. Right angles
or square corners often become rounded because the model's fine detail is
typically lost in the casting process: first during the intricate steps
of precasting and then in actual casting and finishing.
Irregular Shape: Wax Was Pulled from the
Mold Too Early
Often, the factory technician removes the wax from the rubber mold before
it's fully cooled. The result? The item becomes deformed when it's handled,
and the deformation remains in the piece through the casting process.
Errors in the Casting Process
Unfortunately, common defects can also serve as identifying characteristics.
Here are some of the more common defects or characteristics that make a
cast article easy to recognize.
The surface of a cast article (sometimes referred to as a "skin")
is slightly granular and lacks luster.
Assemblies of Two-Color Castings Don't
It's difficult to cast one piece of jewelry requiring two alloys of
different colors (such as white and yellow gold). Instead, these articles
are typically cast separately then soldered together after prefinishing.
Too often, the joining is not done with precision.
Pits are the result of errors in workmanship and poor or inadequate casting
Next month: Tom Weishaar, JA's first Certified
Master Bench Jeweler, will discuss issues surrounding porosity.
Illustrations by Lainie Mann
JA Quality Assurance Guide
Integrity of Cast Jewelry
Properly Cast Jewelry
Here are the signs of a properly cast article of jewelry.
- The appropriate alloy is used.
- The article's detail and pattern are maintained.
- The design and alignment of components are consistent.
- The piece is free of porosity (no small-to-large pits or cavities on
Ring Too Thin and Lightweight
This may be a second-, third- or fourth-generation reproduction. Molds
for this ring were made from reproductions, resulting in rings far too thin
and lightweight for normal wear.
This ring has visible pits on the surface of a highly polished area;
pits result from errors during the casting process. There is no remedy
the ring must be redone.
As a result of errors in the casting process, the ring has cracks in
the prongs (a critical point) and another very visible one on the shank.
There is no remedy
the ring must be redone.
As a result of errors in workmanship when finishing a cast ring, small
nodules can appear inside the shoulder of a shank.
Mold lines that occurred when wax was injected into the rubber mold before
casting still show on the side of this ring. It would be impossible to remove
them without destroying the ring's design.
© Jewelers of America
This information is required for the second through fourth levels of
certification (written tests) for the JA® Bench Jeweler Certification
program and the first and second levels of the JA® Sales Professional
Illustrations by Lainie Mann
Copyright © 1999 by Bond Communications.