One of the first things to catch my eye at the Musee Picasso in Paris was this: the actual copper plate for his etching Weeping Woman, derived from the great painting of the same name. They also had proof prints taken from the plate:
It's rare to see the actual copper plates (often because they are supposed to be scored with a big 'X' at the end of en edition, and destroyed). so this was a treat for a printmaker such as what I am. My first thought as to why the plate is so dark: the final layer of ink or resist was left on the plate in the 1940s, and it's hardened over the years. But maybe it was steel-faced, a process that prolongs the life of a copper etching (because copper is a soft metal and wears down much more quickly than steel.)
What's great about seeing the plate is how close you get to the process of creation, as you can see every etched line, and engraved line, and ragged fuzzy drypoint line:
You also get a real sense of the force of Picasso's hand as he gouged all those winding lines deep into the surface of the plate. Especially in close-up, you can see how varied the width of the lines are, and how playful and improvised the drawing is.