To the Editor:
In the October 1995 issue of Alkaline Paper Advocate on page 47 [and also on p. 87 of the November Abbey Newsletter], it was suggested that 1000 year old waterlogged wood from a shell midden in British Columbia had been preserved because of the alkaline conditions therein. (Shell middens are presumably alkaline because of the high content of calcium carbonate present.) The implication is, presumably, that if alkaline conditions have preserved archaeological wood--a lignocellulosic material--they probably also preserve paper.
I think it is extremely doubtful, however, that the alkaline conditions were an important factor in the preservation of the archaeological wood in this situation. I also think that anaerobic burial in waterlogged conditions is such a dissimilar environment from that experienced by books or documents in archives or libraries that no implications can be drawn from the comparison.
At the Canadian Conservation Institute, I spent a number of years examining the problem of waterlogged wood. During that time I saw preserved wood from many parts of the world and from many environments. On examination and analysis it quickly becomes clear that the chief threat to its survival is biodeterioration and not acid degradation. For example, when wood is maintained in a dry state, it remains perfectly intact for remarkably long periods--witness the boat beneath the pyramid of Cheops in Egypt which is on the order of 4650 years old. The wood from that ship is in a remarkably good state because fungal and bacterial action have been very limited in their effects.
Wood from waterlogged archaeological sites is, without exception, preserved in anaerobic, usually acidic conditions. In this state fungal activity is halted. Biodegradation continues very, very slowly as tunnelling bacteria invade and gradually consume the S2 layer of the cell wall. This form of attack causes the gradual destruction of the cellulose component of the wood. Hence very old waterlogged wood, such as the 5,000 year old material from the Somerset Levels in England, is found to be composed almost entirely of lignin.
Perhaps the most extreme example of preservation is the 40 million year old wood found in the Canadian Arctic on Axel Heiberg Island N.W.T. Typical samples bear almost no trace of mineralization. One example contained about 35% easily recognizable cellulose and 65% lignin. The burial conditions in sands and silts rich in quartz poor in mineraliferous material were acid rather than alkaline.
I use these examples not to show that acid degradation does not occur in wood--I think there is evidence that it does--but to emphasize that wood is different from paper. You simply can not draw conclusions about the stability or instability of ligneous paper from wood. The processing of paper fundamentally alters the nature of the materials and furthermore the environment of preservation of archaeological wood is totally unlike that of books or documents. One might add that our observations of archaeological wood show that lignin and cellulose, if free from chemical intervention by humans, are among the most stable organic materials known.
I hope this is a useful comment. I would be happy to supply further information on this topic.David Grattan
[The article Dr. Grattan refers to is entitled "Carbonate-Filled Groundwood for Cash-Strapped Publishers." I had written this article because I had heard that certain publishers who had switched from acidic groundwood to alkaline freesheet in the late 1980s had gone back to acidic groundwood when the price of paper nearly doubled last year. I wanted them to know that carbonate-filled groundwood, a recent innovation, is a better alternative than the old kind of groundwood. It is readily available, economical and apparently long-lasting, except for a tendency to yellow. -Ed.]
Editor's reply to David Grattan:
The passage you refer to in your letter was the following paragraph:
In the last five years or so, however, alkaline groundwood grades have been appearing on the market. They contain calcium carbonate, which can preserve almost anything. Archaeologists have dug up rare wooden artifacts on the east coast of Canada that were over 1000 years old, preserved only because they were in a midden of discarded sea shells rich in carbonate. One can safely say that carbonate-filled groundwood is better than acidic groundwood, even if it does not meet the requirements of the ANSI/NISO or ISO permanence standards.
Notice that I have said nothing about the west coast of Canada, or waterlogged wood, or the relative keeping qualities of cellulose and lignin. The excavation I referred to was the subject of a science program on public TV last fall. The narrator emphasized that wooden implements like those found in the excavations described, rarely last as long as these did, but these were in a calcium carbonate environment. Tools of bone and antlers, he said, are more often found in archaeological excavations, because they do not decay as readily underground as wood does. The archaeologists speculated, if I recall correctly, that these could have been the "red paint people" whose settlements have been excavated elsewhere in New Brunswick. At any rate, the implements showed that these people made their living by fishing rather than by farming or hunting.
I have tried to find a reference in the literature about this dig, but so far without luck. The public TV people cannot supply the information until they know the name of the program, because they do not index their programs by subject. However, I can refer you to Jim Tuck, an archaeologist in the Archaeology Unit at Memorial University in Newfoundland, who has worked in that part of Canada for a long time and seen a lot of shell middens. He may be able to confirm my statement about shell middens and wooden implements. There is also a book that I have not seen yet, which I suspect will bear me out: Archaeological Wood: Properties, Chemistry & Preservation, by Roger M. Rowell, published recently by the American Chemical Society.
I did not conclude from that TV program that groundwood paper would last longer if it was carbonate-filled. I have known this for many years, having seen how well deacidified newsprint performs in aging tests. I simply thought that the publishers would get the point more quickly if I drew a simple and dramatic parallel between that buried wood and the buffered groundwood I wanted them to use. Most publishers, after all, have never even heard of deacidification research involving groundwood. That article was written for the benefit of publishers.
There was a statement in that article, however, that I would like to correct right now. It is in the next paragraph: "Carbonate can not keep groundwood from yellowing, but for some purposes that may not be very important." In fact, there is evidence that it does retard darkening. The groundwood samples, for instance, in the second Lee/Bogaard/Feller publication (under 3B1.24 in the Literature section of the last issue) darkened much less after light exposure when they had a high pH in the 9 or 10 range, which is where precipitated calcium carbonate would usually put it. So even if carbonate does not prevent yellowing of groundwood, it can slow it down considerably.Ellen McCrady