I did a bit of painting the other day. I could not find a palette so I used a ruler. I forgot to wash the paint globules off and when I got home they had dried up. Acrylic is near impossible to wash off. The ruler is rendered useless. But it is now colourful and rather pretty. The globules are cool to the touch. The ruler sits on a stack of books on my table. I figured my doddy wouldn't come looking for a ruler there. (It's his ruler.)