I have a new favorite tool, and this is my first experiment with it; want to know what it is? Watch for the surprising answer in June!
ANSWER TO MYSTERY TECHNIQUE #58:
This is part of a painting test I did for a flexicube called Six Sides of Science. The patterns of lines on each side were inspired by the veins and arteries in old medical diagrams, and 2 of my line-making tools are pictured below: my favorite liner brush (brand unknown) and a Fluid Writer (by Kemper). I used diluted layers of acrylic inks and Hydrus liquid watercolors with Granulation Medium for the background colors; then I drew some of the lines with water only before adding diluted acrylic for the veins.
Here are 2 views of the completed flexicube, which won a Purchase Award several years ago.