In proofing the felt, the fibres become
varnished over with a kind of glaze which is insoluble in water, and
this varnish or proof is but imperfectly removed from the ends of the
fibres on the upper surface of the felt. The consequence is a too slight
penetration of the dyestuff into the inner pores of the fibres; indeed,
in the logwood black dyeing of such proofed felt a great deal of the
colour becomes precipitated on the outside of the fibres--a kind of
process of "smudging-on" of a black pigment taking place. The subsequent
"greening" of the black hats after a short period of wear is simply due
to the ease with which such badly fixed dye rubs off, washes off, or
wears off, the brownish or yellowish substratum which gradually comes to
light, causing a greenish shade to at length appear. If we examine under
the microscope a pure unproofed fur fibre, its characteristic structure
is quite visible. Examination of an unproofed fibre dyed with logwood
black shows again the same characteristic structure with the dye inside
the fibre, colouring it a beautiful bluish-grey tint, the inner cellular
markings being black.
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