What's the composition of the sludge that results from dipping an aluminum plate into a bath containing equal parts copper sulfate and table salt?
For more background, I recently went on an etching course where this is the method that we used to etch the aluminium plates that we were going to print from. I was curious about the chemical composition of the reddish stuff that bubbled up everywhere that we hadn't blocked off the plate with some sort of resist.
Printmakers also use zinc plates in a copper sulfate/table salt bath, and I was wondering what chemical sludge would result from that combination.
Many thanks in advance for any light you can shed!