Argentium sterling silver

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.

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 University. The project began in 1990 with research on the effects of germanium additions to silver alloys. Germanium was discovered to impart the following properties to sterling silver :

• Firescale 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 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 solidus 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

A double-cone 3D model of colour. The dark to light axis is the one used to measure the tonal value of tarnish..

Tarnish resistance is measured through a scientific process using the CIELAB standard colour measurement system. A 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.

References

• Eid, Cynthia (September 2006). "Road Testing Argentium Sterling". Art Jewelry: 25–33. 
• "Firestain—The Nemesis of the Silversmith". The Goldsmiths' Company 'Technical Bulletin', Issue 3: 10–11. April 2006. 
• Haag, Terry (February 2006). "Shine On Silver". Jewelry Arts & Lapidary Journal: 20–24. 
• Martin, Eva (2006 2006). "Step by Step—Argentium Silver Box Clasp". Jewelry Arts & Lapidary Journal: 36–42. 
• Edge, A. M.; V. E. Edge and J. J. Edge (2005). "Investigation on the Quality of Enamel on Germanium Silver". The Goldsmiths' Company 'Technical Bulletin', Issue 2: 8–10. 
• Eid, Cynthia (July 2005). "Argentium Sterling Silver". SNAG (Society of North American Goldsmiths) Technical Newsletter 13. 

External links

• ArgentiumSilver.com (requires Adobe Flash)
• Argentium.eu (offizielle German Site)
• Society of American Silversmiths
• US Patent 6,168,071