nutgall

I was unable to locate any of the ordinary astringent drugs, such as kino, krameria, or nutgall.

Still more durable and resistant to soap is the preparation if fine nutgall is mixed with the phosphoric acid and water solution.

I found the best material in phosphoric acid, especially when mixed with finely crushed nutgall.

Nutgall gives even the other acids the property of resisting soap more than ordinarily.

One way is to grind the stone rough, pour diluted aquafortis and nutgall over it, clean it with water and dry it.