AIC's 52nd Annual Meeting

The JIAA is testing and developing means with which to predict the risk of metal corrosion and ways to both prevent and mitigate corrosion that will lead to practical solutions. The goal is to replace interventive conservation treatments involving costly and toxic materials with non-invasive treatments using green and sustainable products, or simply by controlling the environment on the micro scale when climate control is not available. Our annual minimum and maximum readings in our storerooms range from approximately 32% to 90% RH and 2°C to 40°C. We have developed a protocol that involves testing the voltage, pH, and chloride content of the bronze objects and of their associated soil that provides indications of susceptibility to corrosion. This work was published in the JAIC this year entitled “Integration of Laboratory and Field Measurements on Soil and Bronze Artifacts: Facilitating Conservation Treatment and Management of Archaeological Collections”. We found that the bronzes measuring below a certain pH were most susceptible to corrosion. Burial depth has been found to be an important indicator of the porosity and degree of susceptibility of bronzes to corrosion in storage. Different corrosion processes were identified above and below the dripline in the soil profiles of archaeological sites. Recent tests that monitor oxygen depletion of bronze objects in Escal bags have shown the effectiveness of first drying bronze objects with ethanol and the overall effectiveness of this method for predicting corrosion activity. In some cases, desiccants and oxygen absorbers may not be required for the protection of bronze artifacts. Our recent tests involving microclimates show heat-sealed Escal bags can hold their seal for up to 10 years (and perhaps longer) and that silica gel will remain dry in the bags for this length of time. For these reasons the JIAA is switching from the more costly RP-A oxygen scavengers to color-indicating silica gel (to avoid including rather costly RH strips or dataloggers in the bags). Recent JIAA tests comparing cysteine, AMT, and BTA show cysteine as a much more effective corrosion inhibitor and that this inhibition may be lost through handling or by wetting the object. Corrosion inhibitors may be reserved for those objects destined for display in the museum when climate control is inadequate or non-existent. We have begun testing iron objects to determine if similar means of risk detection and prevention may be applicable. Our student interns have been testing green corrosion inhibitors such as garlic, black pepper, and ginger on copper and mild steel. We have had good results to varying degrees with all green inhibitors tested to date. The corrosion inhibitors were initially tested on new metal test coupons and recently we started testing some of them on archaeological bronzes. Five possible options are presented for the preventive conservation of archaeological bronzes: 1)applying chemical corrosion inhibitors, 2)drying bronze objects in ethanol by immersion before placing them in Escal storage bags, 3)storing bronze objects in Escal with a desiccant such as color-indicating silica gel, 4) storing bronze objects in Escal with an oxygen scavenger such as RP-A, and 5) no protective microclimate or treatments necessary based on the determination of low risk for corrosion.