Silver

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  Objects Specialty Group Conservation Wiki

Contributors: Tessa De Alarcon.

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Copyright: 2011. The Objects Group Wiki pages are a publication of the Objects Specialty Group of the American Institute for Conservation of Historic and Artistic Works. The Objects Group Wiki pages are published for the members of the Objects Specialty Group. Publication does not endorse or recommend any treatments, methods, or techniques described herein.

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THIS ENTRY IS A DRAFT

Begin with a brief summary or introduction (1-3 sentences) to your material of object type (most likely the title of your page, for example glass, ivory, basketry ). Don't forget to add images as appropriate!

Materials and technology

This section should be used to provide a basic synopsis or refresher of the topic being discussed. Many materials and object types already have excellent references in the form of journal articles, books, websites, Wikipedia entries, and more. Rather than repeat all of that information here, this is a good place to reference significant publications or resources in summary and refer readers directly to the original sources.

History

If appropriate: brief summary or introduction to historical context, art historic background, function, use, etc.

German Silver: Otherwise known as Nickel Silver, German Silver is a copper alloy with nickel and zinc that has a ‘silver’ appearance. Originally used in China, German Silver was introduced to the western world in the 19^th century by German metalworkers.

Materials

Raw materials; composition; definitions; parts; types; substrate(s); surface decoration; finish; chemical, optical, physical, or thermal properties; etc. *Remember:

Technology

Sources, processing, tools, fabrication, manufacture, design, construction, decorative techniques, etc.

Identification

In archaeological contexts the identification of metals is often general without additional analytical analysis to confirm the metal and its alloying components. The appearance of archaeological silver alloys is variable depending on the alloying elements, and the burial environment. This can make identification on visual examination alone unreliable. For example, silver objects often include some copper and depending on the amount of copper and the chemistry of the burial environment, the copper may corrode preferentially giving the object the appearance of a copper alloy rather than a silver object. Elemental analysis is a more reliable form of identification.

Portable X-ray fluorescence (pXRF) is often used to identify metals and the alloying components but is limited as a surface analysis technique, though it can be used on a cut surface in tandem with other analytical techniques. Typically, pXRF is used for semi-quantitative results unless standards of none compositions, are used to calibrate the results. If a sample is taken for metallographic analysis, the exposed surface can also be used for analysis with a variety of elemental analysis techniques including, XRF and SEM-EDS. ICP-MS (Inductively coupled plasma mass spectrometry), which requires a sample is removed, is also a method that has been used to identify metals and their components.

Manufacturing techniques can be identified using a variety of techniques. For non-invasive analysis, X-radiography is often used to determine if an object is worked or cast as these produce different textures on the X-ray. Working marks such as hammering produces variations in thickness that are often more clearly visible on an X-ray than through visual examination, while a cast object will have a more even and uniform appearance with a slight grain from the casting porosity. An invasive technique that is also commonly used is metallographic analysis. In this case a sample is removed and polished for examination. The sample is also often etched to reveal the metal grain structure which will indicate whether the object has been cast or worked. Cast objects typically have a dendritic structure, while worked and annealed objects have a granular structure. Repeated working and annealing will also affect the grain size (Scott 1992).

Deterioration

Material/object specific issues attributed to physical, chemical, or biological factors including light, heat, moisture, pollution, mechanical damage, faults in the design, poor quality materials, inherent vice, etc.

Conservation and care

This information is intended to be used by conservators, museum professionals, and members of the public for educational purposes only. It is not designed to substitute for the consultation of a trained conservator.

• To find a conservator, please visit AIC's Find a Conservator page.
• To learn how you can care for your personal heritage, please visit AIC's Resource Center.

Documentation

If appropriate: for examination or documentation issues specific to a material or object type, including tips for accurately and meaningfully documenting specific materials, common types of previous repairs or restoration, etc. For general recommendations, please refer to the Objects wiki article on Conservation Practices or for general conservation work practices, please refer to the main AIC wiki section on Work Practices.

Preventive conservation

Dry storage is best for metal alloy objects. One method for addressing active corrosion for metal objects is storage in microclimates, either using a sealable plastic container, or sealing the object in an Escal bag. By using a microclimate, chemical reactions such as corrosion and in particular active corrosion, can be slowed or stopped by removing either oxygen, moisture, or both from the environment. Silica gel is often used create dry microenvironments (Anderson and Riccardelli 2009). The revolutionary preservation system also uses an oxygen scavenger in addition to silica gel (Paterakis and Hickey-Friedman 2011).

Interventive treatments

Topiary camels at Rough Point, Newport, RI

Treatment of archaeological silver alloy objects has varied overtime, particularly in the ways the objects have been cleaned.

Mechanical Cleaning:

This is currently the preferred method for terrestrial sites and involves the use of scalpels and skewers while the object is cleaned under magnification. This method requires practice and skill and is time consuming.

Laser Cleaning:

This has been an area or recent research; however, this may result in micro-melting that could impact potential metallographic analysis.

Electrolytic reduction

This was once a frequently used method for the cleaning of archaeological metals it is less commonly used on terrestrial sites where mechanical cleaning has become the preferred method. In this method the object is immersed in an electrolyte solution and a current is run through the object to reduce the corrosion back to metal.  It is faster than mechanical cleaning but can result in loss of surface leaving areas that appear pitted or spongy. If the electrolyte solution is not changed regularly, it can also result in redepositing copper on the surface, and in worse cases an object may appear plated.

Chemical cleaning

Though no longer the preferred method for cleaning archaeological metals, many collections have objects that have been cleaned using a variety of cleaning methods. It is important to be aware of these treatment histories as it can impact or limit the objects use for analysis and research as the surface and metal composition may have been altered. Some methods used in the past include boiling in formic acid and cleaning with a paste made up of zinc dust and sulphuric acid [5].

References

Use this section for: works cited, bibliography, including websites, external links, etc. Please list references used within the text in alphabetical order, following the JAIC style guide.

Anderson, Gretchen, and Carolyn Riccardelli. "Microclimate storage for metals (and other humidity-sensitive collections): Practical solutions." (2009).

Paterakis, Alice Boccia, and Laramie Hickey-Friedman. "Stabilization of iron artifacts from Kaman-Kalehöyük: a comparison of chemical and environmental methods." Studies in conservation 56.3 (2011): 179-190.

Scott, David A. Metallography and microstructure in ancient and historic metals. Getty publications, 1992.

Further reading

Use this section for: additional references or resources not cited in the text, external links, etc. For references please follow the JAIC style guide.

Brief annotations are allowed to the extent that the subject dictates.

In regard to Wikipedia articles, for some purposes (particularly academia) Wikipedia may not be an acceptable source, but it does provide an easily accessible online reference. Please see the following article for advise on the appropriate usage of Wikipedia and other encyclopedias: Citing Wikipedia.

This article also explains Wikipedia's "cite tool", which should be used to properly cite an article if it is deemed to be an appropriate reference.

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