At 2:19 pm ((PDT)) Mon Aug 6, 2007, in Digest 2254 Gordon Couger wrote:
>Why not just a brush and a few coats of India Ink
Except that India Ink is lampblack (carbon)
suspended in gum arabic solution.
In solution the gum arabic acts as a colloidal
suspension medium and in the dried ink as a
binder to retain the carbon particles.
Gum arabic is a reversible colloid, so the ink
will wash off again in water (or etchant).
Like albumen and gelatine, it has been used
successfully in photographic processes for
lithography and print-making, so it is possible to
turn it into an etch resist by chemically tanning it
or heat-curing it.
However, with Indian Ink that still leaves the film
punctured by millions of porous carbon granules
which make it more liable to failure - a mechanism
which may also explain in the direct inkjet printing
pcb process the poorer performance of black
pigment ink compared with colour inks.
Regards, LenW
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