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 (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.
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.
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.
ICON HLF Intern in Preventative Conservation
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