I always wanted to try coffee painting and I finally did it. The instant coffee I drink isn't very concentrated but I noticed if I put many layers of coffee on the already coffee wet surface it makes it even darker.
Not too different than watercolor except the fact that it doesnt layer transparency but it isnt too big of a problem for me.
Just that it takes forever to dry, especially the very wet parts so a hairdryer is a must...well...patience too. :)
Also I only used only one cup of mixture since I'm familiar with watercolors .
Here is what I did with a spoon of coffee and some water + Faber Castell sepia liner here and there :