Angier did not speak well at all of the use of Coper Sulfate in bluing. One of its problems is it will "Flash Plate" steel but not with a very adherent plate. Before the development of efficient & inexpensive layout inks many machine shops used to keep a vat of Copper Sulfate solution to dip parts to be layed out in. The layout lines could then be made in the copper & after machining it was easily removed.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra