Armenian bole
A friable, earthy clay, usually of a red color due
to the presence of iron oxide; it consists
essentially of hydrous silicates of aluminum and
(sometimes) magnesium. It is used as a coloring
material and is also applied to the edges of books
during gilding. In the latter use it serves both
to provide a base for the gold leaf and to impart
to it a greater depth and luster. When mixed with
paste and a small amount of oil, it may be used to
sprinkle the edges of books. (335 )
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