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Product Info> Precious Metals
Gold
 Gold is one of the most precious metals in
the world.
It is present in the rivers, seas, and the earth’s
crust and trace amounts are present in plants and animals. It is, however,
difficult and expensive to extract. In modern mining
operations approximately 3 tons of ore are needed to extract
one ounce of gold. The many desirable qualities found in gold, along with its
scarcity, have made it the
most popular metal for use in jewelry today.
Properties of Gold
Gold in its pure state:
- Has a melting point of 1945 degrees Fahrenheit (1063
degrees Celsius). When alloyed (chemically combined)
with other base metals the melting temperature of the resulting alloy is
changed. 18K yellow gold has a melting point of 1675
degrees Fahrenheit and 14K yellow gold has a melting point
of about 1550 degrees Fahrenheit.
Has a specific gravity of 19.33. It is relatively heavy
compared to most metals, such as silver (SG
10.7) or iron (SG 7.8). A notable exception is platinum (SG 21.4).
Is more malleable than any other metal and can be
hammered into foil so thin that it is almost transparent.- Has a unique ductility property allowing it to be drawn
into wire so fine it can barely be seen.
Is deep yellow in color. Its great reflectivity
properties help keep its brightness and color from fading with time.
Will not rust, tarnish or corrode. Gold jewelry
recovered from ancient Egyptian tombs is in the same state as when placed there over
4000 years ago.
Is softer than most other metals. On the Mohs scale of
hardness (which is a measure of a gemstone
or mineral’s resistance to scratching), gold has a hardness value of 2 to 2.5.
Diamond has a value of 10. Pure gold may easily be
scratched. Fortunately, gold becomes harder when alloyed
with other base metals.
Is relatively scarce and therefore expensive. It is
estimated that only 125,000 tons of gold have
been mined the world over since the beginning of time.
- Is able to bond with other base metals. This property
gives rise to the many different colors available
in modern gold alloys.
Fineness (Karat Value)
Since ancient times the purity of gold has been defined
by the term karat, which is 1/24 part of pure
gold by weight. Pure gold is equivalent to 24K. Gold purity may also be
described by its fineness, which is the amount of pure
gold in parts per 1000. For example, a gold ring containing 583
fine gold has 583 parts (58.3%) gold and 417 parts (41.7%) of other base metals.
Federal Trade Commission rules require that all jewelry
items sold in the United States as gold shall
be described by "a correct designation of the karat fineness of the
alloy." No jewelry item less than 10K may be sold in
the United States as gold jewelry.
Fineness of Gold Karats
| United States Markings |
Parts Gold |
Gold % |
European Markings |
| 24K |
24/24 |
100% |
1000 or 999 |
| 22K |
22/24 |
91.7% |
916 or 917 |
| 18K |
18/24 |
75.0% |
750 |
| 14K |
14/24 |
58.3% |
583 or 585 |
| 10K |
10/24 |
41.7% |
417 |
Weighing Precious Metals
The weight of a piece of gold jewelry is a factor that
helps to determine its value. It is important
because it is an indication of the amount of fine gold in an item of jewelry. Grams (g) and pennyweights (dwt) are the units of weight most
commonly used in weighing gold. Gold and silver are almost
always weighted in the troy system of weights where one pound troy equals
twelve troy ounces and twenty pennyweights equals one troy ounce. The
Avoirdupois weight system, where one pound equals 16
ounces, is used in the United States for most everything except
precious metals. The following table summarizes useful weight conversions.
Weight Conversion Table
1 gram (g) = 0.643 dwt = 0.0032 oz t = 0.035 oz av
1 pennyweight (dwt) = 1.555 g = 0.05 oz t = 0.055 oz av
1 troy ounce (oz t) = 31.103 g = 20 dwt = 1.097 oz av
1 ounce avoirdupois (oz
av) = 28.3495 g = 18.229 dwt =
0.911 oz t
PRECIOUS METALS
(GOLD, SILVER, PLATINUM GROUP)
All precious metal weights are given in troy ounce (oz
t); there are 12 troy ounces per
pound (lb. t) in contrast to 16 "regular" (avoirdupois) ounces (oz)
per pound (lb.).
Gold (Au)
Purity or "fineness" denoted by karatage (K);
24 karat gold is pure gold.
12 karat gold is 50% gold and 50% alloyed metal.
Gold will alloy with nearly all base metals (Cu, Pb,
Ni, etc.); different colors of gold are produced
by alloying with different base metals. Common alloys are Ni and Cu.
Gold purity can be tested with inexpensive devices that
measure electrical conduction, or by the older
method of gauging the extent of reaction with dilute acids. Pure gold is inert
with respect to dilute HCl and HNO3; most alloys will
react slowly in these acids. Gold plating or filled can be detected
by testing a scratch in the item.
F.T.C. Guidelines governing
sales of gold and gold jewelry in this country state the following:
1) If Karatage is to be stamped on, it must be at least
equal to that designated or higher, and also
must be accompanied by a trademark.
2) Terms "pure gold" and "solid
gold" can only be used for 24 karat gold.
3) Term "gold" can only be used if gold
content is 10 K or better.
4) Term "gold filled" applies only to items
composed of a layer of gold pressed (not alloyed) onto a base metal where the weight of the gold comprises at least
1/20th of the total weight of the item. Fineness must be
shown by stamp, e.g. "1/20 12k G.F." means the gold layer is 12 karat gold and comprises 1/20th of the
total weight of the item.
5) Term "rolled gold plate" is the same, but
gold comprises less than 1/20 of total weight; e.g. stamped "1/30 12 k G.P."
means 1/30 of the metal weight is from 12 karat gold plate.
6) "Gold electroplate" or "gold
flash" or "gold washed" mean a gold coating that is 10 k or better gold at least 0.000007 inches thick. A variant,
"heavy gold electroplate" (H.G.E.P.) is at
least 0.0001 inches thick.
Pricing and Valuation
Average annual US gold prices for the last 25 years
have ranged from about $160/oz t to more than
$600/oz t.
Current gold market prices
Gold prices for the last ten years have hovered between
$300 and $400/oz t.
Silver (Ag)
Pure silver has a specific gravity of 10.5
"Fine Silver" is 99.9% Ag
"Britannia Silver" is 95.84% Ag
"Mexican Silver" is 95% Ag + 5% Cu
"Sterling Silver" is at least 92.5% Ag;
harder than pure Ag.
U.S. "Coin Silver" is 90% Ag
Vermeil (Vur-MAY) is sterling silver with gold plating.
Crude fineness testing is done with dilute nitric acid.
Silver + dilute HNO3 yields a creamy white
to brown liquid. Alloys containing Cu, Ni, and brass effervesce and yield a
green, yellowish green or bluish green color. More precise
technique involves gauging reaction and resulting
color with Schwerter solution (HNO3 + KCr2 + H2O).
Platinum Group metals (Pt, Ir, Pd, Ru, Rh, Os)
Group of precious metals (platinum, iridium, palladium,
ruthenium, rhodium, and osmium) that share
similar chemical and metallurgical properties.
Most "platinum" used in jewelry is composed
of 90% platinum and 10% iridium, which makes it much harder than pure platinum. 5%
ruthenium serves same purpose.
Much like gold, platinum purity and alloys are commonly
stamped, in abbreviated fashion, on items. Unlike
gold, in the U.S., purity is given relative to 1000 parts (per mil), e.g.
"950Plat" is 95% pureplatinum.
Palladium and small amount of ruthenium is used in
setting heads for platinum jewelry; lighter, less expensive.
Rhodium is used as a plating metal. It gives white gold
and platinum a hard, bright finish and slows tarnish on stainless steel.
Platinum has a specific gravity of 21.45.
The Strengths of Platinum
Beneath its subtle beauty and understated elegance lie
the properties which make platinum truly unique.
Platinum is Strong.
It is the heaviest of the precious metals, weighing
almost twice as much as karat gold. Its strength ideally secures diamonds and
other precious gems.
Even after many years, platinum will not wear away or
wear down. For example, after many years of wear, a gold wedding band's shank
will wear down and become thinner. This is not the case with platinum.
As with all precious metals (gold, silver, etc.),
platinum can be scratched. However, with platinum, there is actually no material
lost from the scratch as there is with gold. If your platinum jewelry becomes
scratched, simply take it to your jeweler for a quick polish.
Platinum is Pure.
In America, platinum jewelry contains either 90% or 95%
pure platinum. By comparison, 18 karat gold is 75% pure and 14 karat is 58% pure
gold. Platinum will never tarnish or lose its rich white luster.
Platinum is Rare.
Ten tons of ore must be mined to produce a single ounce
of platinum. It takes five months to process platinum ore into pure platinum.
Only after this time can skilled hands work their creativity and craftsmanship,
transforming platinum into pieces of wearable art.
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