The manufacturing of jewelry using platinum usually entails greater sophistication and more precise control than does gold or silver. In addition, jewelry which combines platinum with other metals also requires special efforts to maintain control of the relative proportions of each metal. Such control may be especially difficult if the fabrication process involves operations which remove metal, such as faceting or polishing, subsequent to the assembly of two metals.
In seeking to address this issue, the authors explored the applications of density data to the control of jewelry manufacturing processes and also investigated techniques for the accurate measurement of density. In particular, the utilization of modern analytical balances in conjunction with Archimedes Principle was analyzed for reliability and practicality. It was determined that, under controlled conditions, the procedure yields data which are both reliable and useful.
Recent Growth of Platinum Jewelry
Since early in the decade of the 1990s, the North American jewelry industry has witnessed a dramatic resurgence in the use of platinum jewelry applications. This significant growth has been
accelerated in no small way by the extensive marketing efforts of the Platinum Guild International. Certain of platinum's inherent properties, such as intrinsic value, chemical inertness, color and luster, density, durability and
formability, make it ideally suited for jewelry applications. Platinum has long been recognized as the premier material for setting diamonds, but is now also being widely employed for wedding bands, ring shanks and tops, and many
other types of jewelry.
Platinum in Combination with Other Metals
In addition to widespread use as a stand-alone jewelry metal, platinum has also been especially popular with jewelry designers who create products which combine platinum with other
metals, particularly gold. By skillfully combining alloys of varying color and texture, designers have created a whole new world of beauty. In the past, these two-tone or multi-colored products generally utilize two or more
different colored gold alloys which were almost always of the same karat or fineness. Now, however, designers are focusing on jewelry items which combine alloys of platinum and gold. These two metals, together, do indeed create
marvelously beautiful pieces of jewelry. The rich, contrasting colors, and the unmistakable "feel" of platinum are very compelling.
The Issue of Metal Content
A combination of significantly different metals such as platinum and gold, or, for that matter, a composite involving different alloys of silver, palladium or other metals, raises interesting issues for
all facets of the jewelry trade. From the standpoint of the consumer, the value of a piece of jewelry is comprised primarily of factors such as: (1) artistry of design, (2) skill and ingenuity of craftsmanship, (3) choice of
materials, and (4) tasteful and appropriate presentation by the retail store. For the jewelry tradesman, however, the value of an item is more likely to be determined by the spread between cost and selling price. In this
situation, the calculation of value will often require an accurate determination of the weight of each precious metal component. For jewelry constructed of a single, homogeneous precious metal alloy, this determination simply
involves knowing the "fineness" of the alloy and the total weight of the piece. However, when the jewelry item involves a combination of materials, this determination can be considerably more complex.
Complexity of Determining Relative Proportions
The most effective way to determine the relative proportion of each material in an assembled item of jewelry is to carefully weigh each component before assembly and then ensure that
no subsequent fabrication operation changes this proportion. If, however, the design of the item requires that the components be assembled in a semi—finished condition, and then entails subsequent cutting or finishing operations
which remove metal, it may be very difficult to accurately determine just how much of each component remains in the finished jewelry.
An Issue Through the Ages
A Lesson From Ancient History
Despite the venerable legacy of jewelry making for literally thousands of years, modern manufacturers are still faced with many of the same issue which concerned their ancient fellow craftsmen.
Each facet of the jewelry trade has always been concerned with knowing the intrinsic value of the items which are produced and bought and sold. Let's examine this problem from an historical perspective.
King Hieron has a Problem
The story of the king of the ancient Greek colony of Syracuse is a classic example. King Hieron wished to commission the creation of a sacred crown, which probably would have taken the form of a
wreath. The king delivered to the selected craftsman a measured weight of pure gold and instructed that the entire amount was to be incorporated into the finished work.
Eventually, the craftsmen completed the crown and delivered it to the king. The king was pleased with the beauty of the crown, but being somewhat skeptical, he instructed that the crown be weighed. Hieron was greatly relieved when it was found that the crown weight was reasonably equal to the original weight of the pure gold. Subsequently, however, the king became puzzled when it was pointed out that the color of the metal did not have the same hue and luster as the original gold. Could it be possible that some other metal, probably silver, had been substituted for a portion of the king's gold?
Archimedes Develops a Solution
King Hieron then summoned his trusted advisor, Archimedes, whose wisdom and ingenuity had been demonstrated many times, and asked him to test whether the crown did, indeed, contain all the king's
gold. Of course, since the crown was a sacred article, it could not be harmed or changed in any way. According to the story, Archimedes was pondering the king's problem as he prepared to take his customary bath. When he
entered the bathing pool, which was completely full, he noticed that the water overflowed the brim as it was displaced by his body. Suddenly realizing that here, indeed, was the key to solving the riddle of the crown, he is said to
have jumped from the bath and run naked through the streets crying "Eureka, I have found it!" Archimedes took pieces of pure gold and of pure silver that had weights identical to the weight of the wreath. He then
successively immerses the gold, the silver, and the wreath in a container filled to the brim with water and measured the volume of water that overflowed with each material. He found that the wreath displaced more water than the gold
but less than the silver, thereby proving that the wreath contained some other metal which was less dense than gold. Further, assuming that the substituted metal was silver, measuring the amounts of water displaced in the three cases
allowed him to calculate the relative amounts of gold and silver which the wreath contained.
A Bathtub Alone Won't Do
Although Archimedes solved the problem at hand, if the above account is correct, he did not actually use the famous principle that we wish to employ. He used the simpler
concept that a body fully immerses in a liquid will displace a volume of liquid equal to the object's volume. Because of silver's lower density, the gold-plus-silver wreath had a greater volume than the same weight of pure gold; it
therefore displaced more water, upon immersion, than an equal mass of pure gold. Unfortunately, the accuracy of volume measurement directly by fluid displacement is too low to be very useful.
Archimedes Principle
Archimedes Principle goes a step further and allows us to use an object's buoyancy in a liquid to arrive at a much more precise measure of its density, or specific gravity. The Archimedes Principle
states, "A body wholly or partially immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced."
This accuracy improvement is a consequence of the precision available by measuring weight using a modern analytical balance.
At this point the article deals with the theory and mechanics of density testing using the Archimedes Principle. Is also explores specific applications of this testing to typical jewelry manufacturing situations.
The authors determined that density determination by Archimedes Principle using modern equipment yields accurate and reliable information which has a variety of useful applications for jewelry manufacturers. Under various controlled conditions, the statistical reliability of these tests shows a standard deviation ranging from 0.006 to 0.022 grams per cubic centimeter. Taking the average, several tests will further improve the reliability. This process is particularly useful in determining the ratio of metal content for jewelry assembled from components of different alloys.
V3N6
Practical Applications of Specific Gravity Determination to Platinum Jewelry Manufacturing
The Uses and Limitations of Archimedes Principle
Paul N. Nordt III, W. Clark Hill, Kathleen L. Rohr
John C. Nordt Co. Inc
This is an abbreviated version of the original work. For full technical details, please consult the original paper.