A posting on the Cons DistList, May 7, 1996. The author is the chief of the Research and Testing Division of the Library of Congress.
For the past several years, the Preservation Directorate has provided free samples of its manuscript marking inks to curators of paper-based collections. Recently, one of the recipients of our ink samples brought to our attention that the stamped impression was smudged by alcohol. Our Preservation Research and Testing Division confirmed this observation, although they also found that most of the ink remains firmly affixed to the paper. Therefore, we would like to warn other users of our manuscript marking inks that any future conservation treatment of items stamped with these inks should take into account the fact that they contain a significant fugitive component that can be removed by several common solvents. Nevertheless, the stamped ink impression cannot be completely removed by any means without causing significant damage to the paper. That is, the objective of providing security for the items stamped with these manuscript marking inks has not been compromised in spite of the removability of a part of the stamped impression.
The indelibility of the LC manuscript marking inks derives mainly from the small particle size of the pigments used in their formulation. The particle size is so small that these pigments penetrate into the fiber structure of paper. Therefore, these inks cannot be removed from paper without causing noticeable damage. The fact that some of the stamped impression can be removed by solvents means that some of the pigment particles are so large that they remain on the paper surface instead of seeping into the fiber structure. Either the particle size of the pigments has grown during storage due to agglomeration, or the pigment used by the Government Printing Office in the manufacture of the inks did not meet the specification for their formulation. Evidently, we need to investigate this problem. Until a fail-safe solution is found, we shall reluctantly discontinue the supply of the manuscript marking ink samples.