To sole leather there are usually given from one to three
layers of valonia. The demand for valonia is increasing more and more
every year, and the present outlook does not indicate any relaxation
of its popularity. Its use for upper leather is very limited.
Myrabolams are mainly used in England and Austria, and give a nice
light-colored leather, both upper and sole, although rarely used
alone. Their main use is for dyeing purposes. They are indigenous to
the East Indies.
Sumac is so well known that treating of it is superfluous. Its use is
very extensive, and it is a general favorite for light, fine leather,
which is mostly used for colors.
_Gambier_--Is in general use in England and to some extent in Germany.
_Catechu_.--Obtained from India, resembles gambier greatly. Its use is
almost wholly confined to England. It is also consumed by the silk
manufacturers in preference to gambier, for weighting purposes.
PATHOLOGICAL.
We now leave the physiological class and take up those tanning
materials included in the pathological class, or those of abnormal
growth.
_Galls_.--These are not consumed to any great extent at the present
period, but formerly they were used quite extensively. The galls are
found upon the leaves of the oak or sumac, etc. The direct cause of
their growth is that a certain wasp (cynips galles) stings into the
leaf and after depositing its egg, flies away.
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