Tag Archive | Collections Care

How to Protect your Silver

Hello all, I promised a while ago to give you some more details about materials that can be used to protect silver.

There are many products on the market, however not all are suitable for protecting our silver in the store, as we need a long-term solution and therefore a material that will last. One obvious option is to cover each individual object with a tarnish protection layer, such as a surface lacquer; however this is very time consuming and may not be suitable for contemporary pieces, as some have clear instruction by the artist and maker of how they should be kept and cleaned.

There are also M3 anti tarnish strips, they are special absorbent paper strips that absorbs sulphides and other pollutants that cause silver to tarnish. They are placed in a sealed container with an object and last for about six months, so again not really a suitable long term option. So at the moment the following three materials seem to be the most suitable for this project: Tranprufe, Charcoal Cloth and Intercept.

Tarnprufe

Tarnprufe (fig 1) is a textile that has been impregnated with a zinc salt and sodium carbonate that reacts with the hydrogen sulphide (the gas that affects silver, leading to a tarnished surface) in the air and neutralises it. Once all of the reacting molecules have been exhausted, the bag looses its protective purpose. The objects need to be fully covered by the material and some conservators have experienced a 13 year life expectancy. The only down side being there is no obvious indicator as to when the fabric is exhausted, so there is no way of telling if the bag still protects the silver, unless you sent the bags off to be tested in a laboratory but that can be quite expensive.

Tarnprufe bag

Figure 1 shopwing a Tarnprufe bag

Charcoal Cloth

Charcoal cloth (fig 2) works on a similar basis as the Tranpruf bags, but it uses activated charcoal as a mechanism, as it has a large surface area to absorb pollutants. It can be ordered in large sheets with various thicknesses and then cut into the shape that is needed.

It is not recommended to use this material in direct contact with the silver objects, so it is advisable to use a barrier layer such as acid free tissue or melinex.

Charcoal cloth and corrosion intercept

Figure 2 showing charcoal cloth at the bottom and corrosion intercept at the top

Corrosion intercept

This has highly reactive copper particles, bound into a polymer matrix (fig 2). When the copper turns black all the reactive molecules have been exhausted and it needs to be replaced. This is very useful as it enables us to see if the bag needs changing. The manufacture suggests that 1mm thickness will give about 10 years protection.

So far we have put some of the objects into already existing Tarnprufe bags and we are still in the process of deciding how to protect the remaining objects in the store, it probably will be a combination of materials stated above.

I am afraid this will be my last blog as my time at Birmingham Museums Trust has come to an end. I hope you found this blog useful and interesting.

Rosemarie Wachsmuth,
ICON HLF Intern in Preventative Conservation

X-raying an Nkisi Figure

The Collections Care and Conservation Department recently x-rayed an Nkisi figure donated to the Museum in 1935.

Nkisi figure

Nkisi figure (accession number 1935A71.1)

Often human or animal in form, these figures were used by people such as the Songye of southeastern Congo to protect villages, families or individuals from illness and witchcraft and to resolve disputes. Each figure acted as a vessel for ancestral or natural spiritual forces and their use was closely associated with the belief that the dead could influence the fortunes of the living.

Magical substances called ‘medicines’ were stored within the figures. These included clay, charcoal, seeds, animal matter, human hair and nails. Figures could also be adorned with beads, feathers, animal skins or metal nails which further enhanced their powers. The use of nails, often of European manufacture, has been linked to Christian concepts of sacrifice and martyrdom introduced by Portuguese missionaries who arrived in central Africa from the late fifteenth century onwards.

Nkisi figure being place in the x-ray machine

The use of x-ray techniques are important for conservators and curators as they can reveal features beneath the surface of an object that would otherwise remain concealed.

The x-ray of the Nkisi figure clearly shows the internal structure and reveals that in addition to a main stomach cavity, the figure has a secondary cavity (highlighted in the x-ray below) in the lower abdomen which is not externally visible. Both contain bundles of loose organic material. Further analysis is necessary to determine what this material is, but importantly the scan confirms that the figure was produced for ritual use rather than for sale / export – as became the case with many Nkisi figures produced in the 20th century.

X-ray of Nkisi figure with highlighted second cavity

X-ray of Nkisi figure

Side x-ray of Nkisi figure

For more information on x-raying objects, the Collections Care and Conservation Department are running behind the scenes tours on Saturday 28 September. Further details can be found here: http://www.bmag.org.uk/events?id=2878

Adam Jaffer,
Curator of World Cultures