Today I was reading about tattoos (which I do every day, so that's nothing special), and I was reading this piece on the functionality of outlines and why certain tattoos without outlines won't work: it would cause the inks to mix/run over after a good while.
And then what made my day: reading this gave me a revelation on a piece I'm doing for my mother. I was kind of stuck on how to execute it. I'm painting a little sculptures elephant for her, the surface of the elephant is smooth and non-absorbant. Obviously it's also curved. I wanted to paint a couple of pretty flamingos on it, using transparent ink, and I was at loss on how to do this. The ink would just run off the surface if I use it as is. Mixing it with another medium isn't an option either, because this would lose the transparency of the inks. But: outlines! I can use acrylic outlines! Why haven't I thought of it any sooner? Now I just have to rework the design so that it will work when I use lines.