Just like da Vinci

The ink, that is.  The drawing - not so much...

I made walnut ink, as used by Leonardo and cohorts.  The recipe is quite easy.  You gather 30 or so walnuts under a tree in the fall, so they are still in their green or blackening skin (pericarp).  (Beware of jealous squirrels at this step).  Put them (the walnuts, not the squirrels) in a non-metal pot with water and a bunch of rusty nails, and boil. At this point, experienced cooks will be saying "Hey, that's just the recipe for traditional Walnut and Rusty Nail Soup."  True, but the difference is that you boil the ink for 10 hours.  Then you let it sit overnight, sieve out the solids and boil the liquid down until it looks like ink.  It's very pleasant to use, with good gradations where you overlap several layers.  It also lifts well, like watercolour - I've always thought that da Vinci was amazing to do his detailed drawings in ink, where you can't correct mistakes, but actually it's quite easy to almost completely remove a bad line.  Gum arabic might thicken the ink and make the tone more intense, but I haven't tried that yet.  

Now I just have to figure out how to draw like him.  Or maybe I'll stick to designing impractical flying machines.