Argentium sterling silver
Encyclopedia
Argentium Sterling silver is a modern sterling silver
alloy which modifies the traditional alloy (92.5% silver + 7.5% copper) by replacing some of the copper
with the metalloid
germanium
. As it retains the 92.5% silver content of the traditional alloy, it is still referred to as sterling silver.
. The project began in 1990 with research on the effects of germanium additions to silver alloy
s. Germanium was discovered to impart the following properties to sterling silver :
Many of these properties significantly affect the traditional methods of working silver. For instance the absence of firescale
eliminates tedious and time-consuming steps required by the silver worker using traditional sterling silver. It also eliminates the need for plating the final product which is often done on manufactured items because of the problems introduced by firescale. Tarnish resistance is of significant importance to both silver workers and the wearer of silver jewellery.
Argentium Silver is patented and trademarked by Argentium Silver Company, UK.
melting temperature of 1475°F (802°C) and a liquidus flow point of 1650°F (899°C). The solidus melting point of Argentium Sterling silver is 1410°F (766°C) and a liquidus flow point of 1610°F (877°C).
Sulphur test
The sulphur test reproduces the effects of sulphur and sulphurous gases found in the atmosphere and everyday substances. This test is based on a ISO (International Standards Organisation) corrosion testing protocol used within the precious metals industry (ISO 4538:1995).
Perspiration test
This test reproduces the effects of perspiration and skin contact with silver alloys. The testing procedure is based on a standardised procedure used in the spectacles industry (ISO 12870:2004).
Ultraviolet test
The ultraviolet test determines whether alloys are photosensitive to ultraviolet light. This is especially applicable to silver articles that are on display and exposed to sunlight.
is used to measure the change in surface colour on each test sample after exposure to the tarnish tests. The ‘dark to light’ scale (the central vertical axis in the double-cone colour diagram) is the critical measure used to gauge the degree of tarnish film that is formed on the silver alloy test samples.
Argentium alloys are required to pass predefined levels on the ‘dark to light’ scale, using the CIELAB system. The results from all three tests are combined, using the following weighting coefficients, to give a Tarnishing Index value:
The overall test results are charted. AQL - the Argentium Qualification Line - is the minimum tarnish resistance requirement for Argentium silver alloys.
Sterling silver
Sterling silver is an alloy of silver containing 92.5% by mass of silver and 7.5% by mass of other metals, usually copper. The sterling silver standard has a minimum millesimal fineness of 925....
alloy which modifies the traditional alloy (92.5% silver + 7.5% copper) by replacing some of the copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
with the metalloid
Metalloid
Metalloid is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, each element can usually be classified as a metal or a nonmetal. However, some elements with intermediate or mixed properties can be harder to characterize...
germanium
Germanium
Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon....
. As it retains the 92.5% silver content of the traditional alloy, it is still referred to as sterling silver.
Origins and description
Argentium Silver is the result of research by Peter Johns at the Art and Design Research Institute (ADRI), School of Art & Design, Middlesex UniversityMiddlesex University
Middlesex University is a university in north London, England. It is located in the historic county boundaries of Middlesex from which it takes its name. It is one of the post-1992 universities and is a member of Million+ working group...
. The project began in 1990 with research on the effects of germanium additions to silver alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
s. Germanium was discovered to impart the following properties to sterling silver :
- FirescaleFirescaleFirescale, also known as firestain, is a red or purple stain that appears on mixtures of silver and copper, such as sterling silver. At high temperatures, oxygen mixes with the copper to form cuprous oxide and then cupric oxide...
elimination - High tarnish resistance
- Precipitation hardening and simple heat-hardening properties
- Increased ductility
- Increased thermal and electrical resistance (making alloys suitable for welding and laser forming)
- Environmental advantages (associated with not having to remove or plate over firescale)
Many of these properties significantly affect the traditional methods of working silver. For instance the absence of firescale
Firescale
Firescale, also known as firestain, is a red or purple stain that appears on mixtures of silver and copper, such as sterling silver. At high temperatures, oxygen mixes with the copper to form cuprous oxide and then cupric oxide...
eliminates tedious and time-consuming steps required by the silver worker using traditional sterling silver. It also eliminates the need for plating the final product which is often done on manufactured items because of the problems introduced by firescale. Tarnish resistance is of significant importance to both silver workers and the wearer of silver jewellery.
Argentium Silver is patented and trademarked by Argentium Silver Company, UK.
Physical properties
Traditional sterling silver has a solidusSolidus (chemistry)
In chemistry, materials science, and physics, the solidus is the locus of temperatures below which a given substance is completely solid...
melting temperature of 1475°F (802°C) and a liquidus flow point of 1650°F (899°C). The solidus melting point of Argentium Sterling silver is 1410°F (766°C) and a liquidus flow point of 1610°F (877°C).
Tarnish testing Argentium silver
Argentium silver alloys are tested using three laboratory tests. These tests are designed to replicate the effects of environmental pollutants and everyday conditions that cause tarnish.Sulphur test
The sulphur test reproduces the effects of sulphur and sulphurous gases found in the atmosphere and everyday substances. This test is based on a ISO (International Standards Organisation) corrosion testing protocol used within the precious metals industry (ISO 4538:1995).
Perspiration test
This test reproduces the effects of perspiration and skin contact with silver alloys. The testing procedure is based on a standardised procedure used in the spectacles industry (ISO 12870:2004).
Ultraviolet test
The ultraviolet test determines whether alloys are photosensitive to ultraviolet light. This is especially applicable to silver articles that are on display and exposed to sunlight.
Measuring tarnish resistance
Tarnish resistance is measured through a scientific process using the CIELAB standard colour measurement system. A colorimeterColorimeter
For articles on Colorimeter see:* Colorimeter * Tristimulus colorimeter...
is used to measure the change in surface colour on each test sample after exposure to the tarnish tests. The ‘dark to light’ scale (the central vertical axis in the double-cone colour diagram) is the critical measure used to gauge the degree of tarnish film that is formed on the silver alloy test samples.
Argentium alloys are required to pass predefined levels on the ‘dark to light’ scale, using the CIELAB system. The results from all three tests are combined, using the following weighting coefficients, to give a Tarnishing Index value:
- Sulphur - 0.6
- Perspiration - 0.2
- UV - 0.2
The overall test results are charted. AQL - the Argentium Qualification Line - is the minimum tarnish resistance requirement for Argentium silver alloys.
External links
- ArgentiumSilver.com (requires Adobe Flash)
- Argentium.eu (offizielle German Site)
- Society of American Silversmiths
- US Patent 6,168,071