3 RESULTS AND DISCUSSION

In order to examine the distribution and variability of trace elements in foxing spots and clear areas of the book papers, samples were taken from various pages of five books. The copper and iron contents in 18th and 19th century books are shown in Table V. The table also shows the location of the samples taken. There is a trend for darkness of the foxing spot to increase with increasing iron content, apparent in the data. The highest concentration of iron was noted in the center of the spots, with the metal concentration decreasing in the selected sample as the distance increased from the center. Moreover, it was observed that the darker the spots, the more brittle the paper became.

TABLE V THE IRON AND COPPER CONTENT IN 18TH AND 19TH CENTURY BOOKS

The concentration of the trace elements differs remarkably between the foxing spots and clear areas of the book page. It seems that the critical element in foxing spots in these books is iron. The iron content in foxing spots varied from 126 ppm to 29500 ppm, depending on the darkness of the foxing. The iron content in the clear book paper varied from 15 ppm to 515 ppm.

Of the books tested, one was bound by iron staples. This was an Italian book printed in 1891. The paper in the area of the staple bindings contained 2.95% iron. The area around the staples had a significantly higher number of spots as compared to the rest of the page. In general, the copper content in the foxing spot is a little higher than that in nonfoxed areas, except that in one page the foxing spot had 158 ppm copper and the clear areas had 41 ppm copper.

3.1 Copper-Induced Foxing (see Figure 4)

Foxing was observed in paper made in this laboratory. The stock was 50% refined rag/50% Weyerhauser S. G. Kraft, and sized with 1% Hercules Neuphor rosin. Alum was added to a pH of 4.5. Williams freeness of the stock was 300 seconds. Noble and Wood equipment was used in making handsheets. In this equipment, the stock was held in a copper chest, felted in a brass felter, and white water was recirculated from a copper tank. Drying was against a stainless steel drum with a felt belt carrier. The sheet produced was high in copper—98.2 ppm, as shown in Table IV.

Fig. 4. Foxing spots with high copper content

Mrs. Katherine Woodward of the laboratory alkalized the paper by the double decomposition method (U.S.P. 3,898,356), dipping first in 10% sodium carbonate solution, then in 10% magnesium chloride, and finally washing out the byproduct, sodium chloride. Sheets were aged at 100�C in the dry oven and 90�C/50% r.h. in the humid oven. Mrs. Woodward reported that in the sheets before treatment and aging there were pale tan spots. After the ovens, a marked development of brown-colored spots was noted in the untreated paper. This was more pronounced in the paper aged in the humid oven than in the dry oven aged paper. The treated paper, however, showed no spotting at any time in the aging study.

Another example of what must be considered copper foxing was observed in an 18th century French map apparently colored in some areas with a verdigris pigment. L.C. Restoration staff observed that this map was more brittle in the brown foxed areas than in clear areas. A copper content of 1093 ppm was found in these brown areas, as shown in Table IV.

3.2 Precision of the Analysis

Analyses for copper and iron content in books and various papers were based on the average of 3–6 replicates. The results, shown as averages, appear in Table VI. The high standard deviation of iron and copper in books and various papers indicated that the elements are not uniformly distributed.

TABLE VI MEAN AND STANDARD DEVIATION OF IRON AND COPPER FROM BOOKS AND PAPERS