1.Leave small vol. of coffee (~2-3 cm3) in a cup.
2.Swirl coffee around.
3.Tilt the cup ~30o and hold. As coffee runs down some of its particles stick to the bottom.
4.Turn the cup a little, tilt, and hold; repeat until you like formation of particles, or the painting!
This is fascinating; random flows turn into intriguing paintings! Images shown here were cropped to the bottom of a porcelain cup; no other alterations were done to the images.
Best coffee for this purpose can be found in hotel rooms. Individually packaged in a filter bag, fine particles pass through the filter when making coffee.