This month’s storage project—watch out for combinations of metal and wood

Do you have your rings and necklaces stored in a beautiful wooden box? Or wrapped in silk, or lying on woollen felt? You might also own other metal objects, like watches, medals and coins.

Metal and wood are unfortunately often not a good mix. Woods give off organic acids (e.g. acetic, formic), which can react with metals to form tarnish and corrosion. Some combinations are particularly bad—a university lecturer liked to tell us the story of a lead coin collection stored in beautiful old oak cabinets, which, when opened one day, had been found to have turned to the coins to dust. (Or, more accurately, small piles of lead corrosion product—see this image from the Peabody Museum). Probably (hopefully) you do not wear any jewelry made from lead, but other metals can also be affected—e.g. iron, steel, copper, brass and silver. Gold is the most resilient—it doesn’t really tarnish, so if you find tarnish forming on something you believe to be gold it might not really be gold.

Oak, sweet chestnut, Western red cedar and Douglas fir are all particularly volatile woods, though volatility does decrease somewhat with age. Plywood and MDF can also be bad, possibly more from the adhesives used to bind the wood product than the wood bits themselves. Silver tarnishes from contact with sulphur, which may be airborne or emitted from protein-based fabrics like wool and silk.

Good storage materials for metal include other metals (inert metals, that is—powder-coated steel is better than uncoated iron!), inert plastics (polypropylene, polyethylene) and acid-free cardboard and paper. You can probably find some suitable small plastic containers that can fit into your nice wooden box—ones designed for holding beads or tablets might be suitable. Even wrapping your pieces in a cotton hanky or acid-free tissue paper before placing them in your wooden box can help prevent corrosion—direct contact with wood will cause the worst damage. (Avoid coloured fabrics where possible, as some dyes can also be acidic). Silver cloths are a good choice for storing silver objects, as they actively adsorb sulphur from the atmosphere and prevent scratches and bumps. It’s also good to prevent jewelry items from touching each other, in case galvanic corrosion occurs. (This is where one metal corrodes in preference to another, which can occur if they’re in contact and there is moisture around). For that reason, you might also consider storing like with like—steel with steel, silver with silver etc.

Find more information about storing metal objects at the Canadian Conservation Institute, the Australian War Memorial and the Victoria and Albert Museum.

NB This post was originally written for one of our pinknantucket press newsletters. If you’d like to receive more of the same direct to your inbox (but only monthly, don’t worry), you might like to sign up (via MailChimp).

Purchase back issues of our material-themed magazine Materiality (BOOK, TIME, PRECIOUS and SURFACE) from the pinknantucket press shop.

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