Without digging out my book & looking it up don't know what formula C17 is. Does it have a high percentage of copper sulfate?. Copper sulfate in solution can give a "Flash Plate" to steel. As I recall even though Angier gave a lot of formulas which included it he was not really fond of copper sulfate on this account.
I have been told that many machine shops used to have a copper sulfate tank where parts to be laid out were dipped in, giving a thin copper plate that would show the marks. By the time I started the trade in the mid 1960's layout ink (Dykem) was being used almost exclusively.
