About 10 years ago I tried to do this. The gourds should be very
dry- several months after harvesting. I didn't try a big "calabash'
style, but smoother "crook necks" and something that had a shape like a
butternut, as I felt they were easier to turn in the bath with little
disruption. There is a waxy layer on the gourd that will prevent color
from bonding- even push color away in the bath. I sanded it with a
very fine-grit (1000 grit?) sandpaper. I left some of the stem on the
end, and used it to hold the the gourd while turning it. I tried water
colors, and it did work, but iI soaked the gourd in alum first and let
it dry. Then I tried acrylics- and they took really well.
I kept repeating the process, building up the colors with over
marbling. It was fun- gave it to my friend who grew the gourds to make
a rattle with...