_Mildew in Books_ (Vol. ii., p. 103.).--Your correspondent B. suggests
that "any hints as to the cause or remedy of _mildew in books_ will be
most acceptable". I venture therefore an opinion that the cause is to be
found in the defective bleaching and manufacture of the rags from which
the paper is made and the careless or intentional admixture of linen
with cotton rags. The comparatively modern method of bleaching with
oxymuriate of lime, or chlorine in substance, with the ad-libitum and
unacknowledged admixture of gypsum (to give weight and firmness to the
paper) are, I believe, the true causes of the defects in question, which
are to be found more in modern books and prints than in those of an
earlier date, and do not arise from damp, as the term "_mildew_" might
seem to imply, although the same appearance no doubt arises from that
cause alone in the older paper. But paper made and bleached by the
processes I have mentioned will become covered with brown spots, however
dry it may be kept.
I have a folio edition of _La Armeria Real de Madrid_, printed at Paris,
without date, but subsequently to 1838 by the preface. The paper is very
stout and fine, and was free from blemish when I purchased it three
years ago, but at present it is covered with brown patches, and the
beauty of the work destroyed, although it has been kept in a very dry
room.
For such defects I should be equally delighted with B. to discover a
remedy; but I fear that so long as our paper manufacturers study
expedition and economy in preference to quality, the case is hopeless.
The ashes left after the combustion of a sheet of paper clearly indicate
the amount of modern sophistication, and greatly exceed those of more
ancient paper. In fact, some paper may now be classed, with more
propriety, among mineral than vegetable productions. Mildew, arising
from damp in old books, may be arrested, if not removed, by exposure to
light, air, and a dry atmosphere.