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Thanks Alberto.
Quoting Alberto Novo <alt_list@albertonovo.it>:
can't we just dissolve the rosin in alcohol, add the pigment,
grind and then wait for the - irrelevant - alcohol evaporates?
Yes and (many) no...
I tried this and I had a mixture remaining soft for years. One can
solve this problem covering a glass plate with a thin layer of
alcoholic mixture, then scratching it when it is hard enough (weeks,
sometimes months...).
Hence, I don't recommend it. An alternative method is to finely
disperse the pigment in a solution of rosin in the minimum amout of
caustic soda. Then dilute it (more or less for 50 g of rosin, 1 to 2 l
of water) and add some chloridric acid while constantly stirring, until
the solution turns acidic. The abietic acid precipitates, inglobing the
particles of pigment. Filter, dry, then crush the aggregate. Alberto