Talking about old ways of ink and paint the other day in class. This was done on acetate with acrylics. Back in the day it would have been done with vinyl paint, but cartoon color went out of business years ago. I think there is still at least one company in england that still makes vinyl paint.
Another factoid was that most of the ink and paint in the animation industry in the states was done by women. Walt Disney gave a strange explanation, saying that women we better suited to detail work.
I started with a rough sketch, laid the acetate over that and made my line art. You can see on the right where I flipped over the piece to show the paint process. I just went with flat color, no light and shadow. It's a lot of fun but super time consuming to work this way for animation. But with animation you are always running out of time.