How many hours does it take two interns to polish 137 pieces of silver spanning 12 rooms in what we have now affectionately termed the doll “mansion”? The answer: approximately 6 hours. The process is not particularly difficult but it is tedious, especially since many of the pieces are extremely fragile. The majority of the silver pieces are marked as sterling silver, which consists of 92.5% silver and 6.5% copper. This results in a soft metal that is easily bent. However, an advantage of this highly valued alloy is its tendency to avoid tarnish because of its copper component; nonetheless, tarnish does accumulate. Unsightly black tarnish on silver is the result of a chemical reaction between the surface of the precious metal and sulfur-containing compounds in the air, which creates silver sulfide. Sulphur is found in large quantities in areas of high pollution but is also regularly emitted in car exhaust. For this reason, the accumulation of tarnish on silver may seem unavoidable, but there are methods for delaying it.
In a previous blog post, we mentioned how we planned to use lacquer to protect the miniature silver pieces in Nancy McDaniel’s dollhouse, but following further consultation and research, we have realized that the lacquer process may actually do more harm than good for such fragile pieces. While modern lacquers have a seemingly long lifespan of about 25 years, they must ultimately be removed (due to yellowing) and then reapplied. Removal of lacquer is intensive and complicated, requiring hazardous solvents. In addition, the lacquering process takes some time to master, and the consequences of poorly applied lacquer can lead to the silver object appearing patchy or corroded where the lacquer was insufficient. Due to the minute size of the silver objects in the dollhouse, lacquer, which is applied as a spray, could easily blow the tiny forks and knives away, increasing the opportunity for an insufficient application of lacquer.
Ultimately, we chose to go with the standard polishing procedure in combination with other preventive measures. First, we simply polished using a very gentle abrasive. Most conservators use a slurry of water and calcium carbonate, otherwise known as precipitated chalk. However, it is just as respectable to use trusted commercial silver polishing products, such as Twinkle and Wright’s Silver Cream, as we did, to polish your own silver. Some important tips to remember when polishing your own silver are: never use products with ammonia, since it is particularly corrosive for silver; always wear gloves, plain cotton or latex gloves are recommended when handling silver since skin oils and acids can etch into the silver surface; and make sure to always rinse your silver well after polishing because leftover polish residue, often in crevices, can cause disfiguring corrosion.
Instead of lacquering to prevent the quick buildup of tarnish on our now-sparkling silver pieces, we have decided to utilize scavengers in the finished display case. Scavengers are safe chemical species selected for their ability to efficiently absorb and filter airborne pollutants. The desired scavengers contain hydrogen sulfide or activated charcoal. The latter variety comes in powder, granule, and woven forms, all of which we are considering in protecting the miniature silver. The added benefit of these materials is that they are relatively cheap and only need to be changed out every six months to a year, depending on the specific environment. The hope is that by incorporating activated charcoal into the finished display case, where the dollhouse will be permanently housed, not only will the silver tarnishing be kept to a minimum, but all the miniatures within the house will benefit from the filtered air.
Post by Karissa Muratore and Amanda Kasman, University of Delaware Art Conservation undergraduates doing a summer internship at Winterthur Museum
(Note: All information regarding silver treatment came from Bruno Pouliot in person and via an article; Pouliot, Bruno P. “A Conservator’s Advice on How to Care for Your Precious Silver.” Silver Magazine Nov.-Dec. 2004: 19-21. Print.)