“Aquatint” is a method for creating areas of even tone, similar to watercolor washes, on an etching.
In fact, early printers called it “aquatint” because its effects reminded them of watercolor. Artists as diverse as Goya , Picasso, David Hockney, and Chuck Close have done great things with aquatint.
It starts with a metal plate, powdered rosin, and an aquatint box.
This is rosin. It’s made by boiling pine stumps and distilling the resin. (Not by me! I leave that job to the experts.) Those lumps look like rocks, but rosin is very brittle. You can easily pound it into powder.
The finer your powder, the more delicate your etched tones will be, but pound it too fine and you won’t have much tone at all. It’s good to mix some coarse powder in with the fine stuff.