Coins from a Time Capsule
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CCI Newsletter, No. 34, December 2004
Coins from a Time Capsule
by Robert L. Barclay, Senior Conservator, Treatment and Development Division - Objects
Figure 1. 1886 one-cent coin, obverse, before treatment.
Figure 2. 1881 quarter, obverse, before treatment.
Figure 3. 1886 one-cent coin, obverse, after treatment.
Figure 4. 1881 quarter, obverse, after treatment.
July 2003 was the centenary of the building of the United Church in Manotick, Ontario. In July1903, a time capsule filled with memorabilia was inserted ceremonially behind the church's cornerstone. When it was removed from its century-long resting place last summer, the time capsule proved to be a stoppered glass bottle in which could be seen tightly rolled documents. Since Time Capsules (CCI Notes 1/6) was published, the process of opening such containers has become a little less problematic for people who have not dealt with this kind of material before. Nevertheless, help from CCI was welcomed because the ground-glass stopper of the bottle was sealed with a resinous material that resisted opening. On testing, the sealant proved to be gum arabic. Gentle warming and application of a little moisture soon released the stopper. Among the newspapers, journals and handwritten material carefully removed from the bottle were several coins of the period.
As is common in time capsules, deterioration of the acidic paper documents within the closed environment had caused the metal objects to corrode significantly. Figures 1 and 2 show the copper and silver coins as they came out of their resting place between layers of paper. The copper coins were covered with a crusty green corrosion layer, completely obliterating their designs, while the silver had a thinner, black layer of corrosion. At first sight, such coins can be disappointing to the officials who are present at the opening, especially the copper ones, which in this case appeared to be beyond recovery. It was the general consensus that nothing could be done with them. However, microscopic examination showed that beneath the loose, crystalline surface the original features were remarkably intact. This is a common feature of copper objects. With judicious chemical treatment and careful work with picks and scrapers, much of the original surface can be recovered. CCI's most recent publication (Metals and Corrosion: A Handbook for the Conservation Professional) provides a wealth of examples of corrosion products with accompanying colour pictures. It also gives insight into the complicated and intriguing nature of metals and their reactions with the environment.
Once the identity of the corrosion on the Manotick time capsule coins had been established, treatment was fairly straightforward. For the copper coins, a dilute solution of sodium sesquicarbonate was applied to each one. Once it had begun to react, the corrosion products could be gently picked away.
When the original features had been revealed, an application of mild metal polish brought back the shine. Figure 3 shows one of the one-cent coins after treatment. The blackened surface of the silver coins was easier to treat. The corrosion was gently removed with silver polish on a small cotton swab, resulting in an almost perfect return to the original bright appearance, as the quarter in Figure 4 shows.
