To date, the most numerous artifact type recovered has been ceramics. Well over 90 percent of the ceramic collection consists of unglazed coarse earthenwares. Conservation treatments, therefore, have been minimal: removal of soluble salts, organic stains, and some marine growth.
The most effective treatment for removing stains (tannin and/or metallic sulfides) has been immersion in hydrogen peroxide or citric acid. Hamilton recommends immersion in 10-25% hydrogen peroxide for 24-36 hours (1994:19). In practice, however, it was found that a three percent solution was very effective in removing organic stains in a relatively short time (1-3 hours). A three percent solution of hydrogen peroxide is very inexpensive and can be obtained locally at any grocery or drug store. More stubborn stains (black metallic sulfides) and some adhering marine growths required treatment in citric acid (5 percent) for anywhere from three to forty-eight hours.
A few ceramics were found with varying amounts of iron oxide corrosion products adhering to their surfaces. These required mechanical cleaning with dental picks and soaking in five percent solutions of EDTA (ethylene diamine tetraacetic acid [di-sodium salt]) or oxalic acid. The use of oxalic acid was terminated when it proved too effective and over-cleaned one fragment of tin-glazed earthenware. Fortunately, the few glazed ceramics that were recovered appeared to be less susceptible to staining and usually only required rinsing.
A number of Spanish olive jar fragments retained traces of pine resin or pitch on their interior surfaces. If these sherds were allowed to dry the resin would spall off from the surface. Consolidation with PVA (polyvinyl acetate) or acryloid B-72 was impractical since the resin dissolved in alcohol, acetone, or toluene. Therefore, the water soluble consolidant, PVAL (polyvinyl alcohol) was added to the final rinse water. A fifteen percent solution of PVAL/distilled water effectively consolidated the resin to the sherd.
Soluble salts were removed after cleaning by placing the sherds in a series of distilled or de-ionized water baths. Rinsing continued until conductivity readings stabilized below 20µs as monitored by a conductivity meter.