Precious Metals and Alloys Purity and Melting Points

Precious Metals and Alloys

What Are Precious Metals?

Gold, Silver, Platinum, and Palladium are considered to be the “Precious Metals.” Other metals and alloys can be found in jewelry components, so their properties are also included below.

Gold Purity

The purity of gold is measured in Karats (US) and in terms of fineness (European). Pure gold is 24 Karats or 1000 Fineness. The process of understanding what exactly a Karat is becomes rather simple when gold is thought of as an alloy (a mixture of various metals) where the karats define the percent of pure gold in the alloy.

US Karat	Percent Pure Gold	European

10K	41.67%	417
14K	58.33%	583
18K	75.00%	750
24K	99.99%	999

Nothing less than 10 Karat gold can be legally marked or sold as gold jewelry in the United States. The legal requirements for minimum gold content vary widely country-by-country. The European markings relating to karatage will be marked in the numbers shown in the above table. Some antique gold items made in the USA may also be marked with the European values.

Colors of Gold

Gold alloys, aside from strengthening gold for jewelry, can also affect its color. The following table shows the most common colors of gold alloys and the metals used in making them.

Color of Gold	Additional Metals Used

Yellow Gold	Copper, Silver, Zinc
White Gold	Nickel, Zinc, Copper
Rose Gold	Copper, Silver
Green Gold	Silver, Zinc, Copper

Silver Purity

In its pure form silver is almost as soft as gold, and therefore is usually alloyed with copper for strength. Karatage is not marked because, legally, anything called Silver or Sterling Silver is 92.5% pure. This is why you will find a stamped marking of 925 on silver items. Due to the fact that silver tarnishes easily, some manufacturers may place a plating of palladium or rhodium over the silver to combat this problem. Please be aware of what you are actually buying.

German Silver or Nickel Silver

This is not the silver we know in the USA. It is a metal alloy of copper with nickel and often, but not always zinc. It is named for its silvery appearance, but contains no elemental silver unless it is plated. Other common names for this alloy are Nickel Silver, Paktong, New Silver, and Alpacca (or Alpaca).

Many alloys fall within the general term of German Silver. All contain copper and nickel, while some formulations may additionally include zinc, antimony, tin, lead, or cadmium. A representative industrial formulation, Alloy No. 752, is 65% copper, 18% nickel, and 17% zinc. The white alloy of 75% copper and 25% nickel used in coins, such as the United States nickel, is better known as copper-nickel, cupro-nickel or cupronickel.

Some nickel silver alloys, especially those containing high proportions of zinc, are stainless, or corrosion-resistant. German Silver is often used in European countries, so please be sure of what type of silver you are getting before purchasing it.

Nickel silver alloys are commonly named by listing their percentages of copper and nickel, thus German silver 55-18" would contain 55% copper, 18% nickel, and 27% other elements, most probably entirely zinc. A two-element alloy may be named for its nickel content alone, thus NS-12 is 88% copper and 12% nickel.

Platinum Purity

Platinum is counted in 1000 parts. Most pieces are 95% pure, or 950 parts per thousand. For guaranteed quality, look for the marks 950 Plat, 950 Pt, Pt 950, Plat, 900 Pt, Pt 900, or 900 Plat.

Platinum jewelry is hypoallergenic, which makes it safe for even the most sensitive skin. The metal resists tarnish and, because of its purity, is one of the strongest, most durable metals in the world. Today, platinum jewelry is commonly alloyed with copper, titanium, palladium, rhodium, ruthenium, iridium, and osmium.

**If you are allergic to 14K gold, you might want to try wearing 18K gold jewelry. Some French hook style earrings are available in hypoallergenic metals, such as surgical steel, instead of silver, and surgical steel plated with 24K gold, instead of 14K or 18K gold. Some additional metals are also used for this purpose, such as titanium and niobium.

Melting Points of Metals and Alloys

Metal	Melting Point (F)*	Melting Point (C)*

Aluminum	1220 (F)	660 (C)
Antimony	1167 (F)	630 (C)
Beryllium	2462 (F)	1350 (C)
Bismuth	520 (F)	271 (C)
Cadmium	610 (F)	321 (C)
Carbon	--	--
Chromium	3326 (F)	1830 (C)
Cobalt	2696 (F)	1480 (C)
Copper	1981 (F)	1083 (C)
Gold (Fine 24K)	1945 (F)	1063 (C)
18K (Green)	1810 (F)	988 (C)
18K (Yellow)	1700 (F)	927 (C)
18K (White)	1730 (F)	943 (C)
18K (Rose)	1655 (F)	902 (C)
14K (Green)	1765 (F)	963 (C)
14K (Yellow)	1615 (F)	879 (C)
14K (White)	1825 (F)	996 (C)
14K (Rose)	1715 (F)	935 (C)
10K (Green)	1580 (F)	860 (C)
10K (Yellow)	1665 (F)	907 (C)
10K (White)	1975 (F)	1079 (C)
10K (Rose)	1760 (F)	960 (C)
Iridium	4449 (F)	2454 (C)
Iron (Pure)	2795 (F)	1535 (C)
Lead	621 (F)	327 (C)
Magnesium	1204 (F)	651 (C)
Manganese	2273 (F)	1245 (C)
Molybdenum	4748 (F)	2620 (C)
Nickel	2645 (F)	1452 (C)
Nickel Silver	2030 (F)	1110 (C)
Osmium	4892 (F)	2700 (C)
Palladium	2831 (F)	1555 (C)
Phosphorous	111 (F)	44 (C)
Platinum (Fine)	3224 (F)	1773 (C)
15% Iridio Plat	3310 (F)	1821 (C)
10% Iridio Plat	3250 (F)	1788 (C)
5% Iridio Plat	3235 (F)	1779 (C)
Rhodium	3551 (F)	1955 (C)
Ruthenium	4442 (F)	2450 (C)
Silicon	2588 (F)	1420 (C)
Silver (Fine)	1761 (F)	961 (C)
Sterling	1640 (F)	893 (C)
Coin	1615 (F)	879 (C)
Tin	450 (F)	232 (C)
Zinc	787 (F)	419 (C)

(F)* Fahrenheit

(C)* Celsius (Centigrade)

Source: “Jewelry Making For Schools Tradesmen Craftsmen” by Murray Bovin Revised Edition by Peter M. Bovin

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