4 CONCLUSION

WATER USED for washing paper artifacts should be free from chlorine and iron and copper compounds, all of which accelerate the deterioration of cellulose. When these potentially harmful substances are removed by distillation or deionization, however, the solvent power of water is increased. Purified water cannot be regarded merely as inert or unreactive. In fact, samples of papers treated in either distilled or deionized water showed decreased levels not only of copper and iron, but also of calcium. This decrease in calcium content seems to have caused the treated samples to perform less well than the untreated samples in accelerated aging tests.

In contrast to purified water, when calcium ions were present in the wash water the treated samples showed a marked improvement in accelerated aging tests, even though the levels of copper and iron were also higher. Washington tap water happens to contain the highest concentration of calcium ions of any of the waters used, even more than purified water passed through a calcium carbonate column, and produced the highest levels of calcium in the washed samples. Therefore, the samples treated in ordinary Washington tap water often performed best in the accelerated aging tests, but the variability and unreliability of tap water both in Washington and in other parts of the country prevent us from recommending it as the preferred type of water.

These tests were conducted in relatively new acid papers which also happened to contain small amounts of calcium. Since washing in purified water, however, may actually decrease the calcium content of paper, we recommend that water should not only be purified but also have calcium ions added to promote the permanence of the paper. One method for accomplishing this is to allow deionized water to flow through a column of calcium carbonate chips before using it. All piping used for purified water should be pvc or polyethylene, not metal.

ACKNOWLEDGEMENTS

WE WISH TO THANK Dr. John C. Williams, Research Officer, and Mr. Peter Waters, Restoration Officer, for their support, guidance, and many practical suggestions during the course of this work. We also wish to express our appreciation to our colleagues in the conservation field who generously answered questions and shared with us their experiences with water washing.