Tarnishing of Sterling Silver
Sterling Silver is often used for making jewelery and decorative items. However, one common problem with silver is surface oxidation, or "tarnishing". To prevent or at least reduce this effect, various alloy elements are added to the silver.
Usage of Silver Alloys
Silver is used in the production of numerous decorative items ranging from jewelery to accessories to musical instruments and fine cutlery; its bright color makes this metal particularly attractive for such applications. The most popular alloys consist of silver and copper with typical millesimal fineness of 825, 925 (Sterling), or even 935 parts silver per thousand by mass. Cu is added to improve the strength and workability of the material.
Oxidation in Precious Metals and Alloys
Though silver is a precious metal, it has a strong tendency to oxidize on the surface, discoloring its bright, glossy face with a dark, dull stain. This effect, called tarnishing, also occurs in copper-alloyed silver.
Improving Silverโs Tarnish Resistance
Therefore, the focus of much R&D has been to improve silverโs tarnish resistance through the addition of small amounts of a variety of elements, including precious metals such as Palladium and semimetals like Germanium, among others. While this vast range of possible alloys makes analyzing the silver challenging, X-ray fluorescence instruments allow for quick, accurate, non-destructive analysis. Fig. 2 shows sections of spectra of various such alloys.
The Right Measurement Technology for Silver Alloys
For such special alloys reference materials for the calibration of XRF instruments are not always available. Therefore it is particularly important to be able to perform uncalibrated (standard-free) measurements that lead to high-quality, reliable results.
| Ag | Cu | Ga | Ge | Pd | Sn | In |
|---|---|---|---|---|---|---|
| 932 | 65.8 | 0.1 | 0.2 | n.d. | 1.3 | 0.3 |
| 913 | 59.5 | 0.4 | 0.2 | n.d. | 3.3 | n.d. |
| 898 | 37.3 | 6.0 | 0.2 | 31.5 | n.d. | n.d. |
| 928 | 56.7 | 0.1 | 12.1 | n.d. | 2.1 | 0.1 |
| 922 | 39.5 | 0.1 | 0.1 | n.d. | 0.1 | 5.0 |
Precise Purity Measurements with Fischer Measurement Technology
FISCHERSCOPEยฎ X-RAY XANยฎ 250 instruments are optimally suited for visualizing even the subtlest differences in silver alloys. They allow precise purity measurements as well as the exact determination of tiny amounts of tarnish-resistant materials and other alloy components. For more information please contact your local FISCHER representative.
