Creativity is allowing yourself to make mistakes.
Art is knowing which ones to keep.
[Scott Adams]
This is a carbon-dust rendering — a method used to give a continuous-tone, photographic effect to a drawing. The shaded areas are built up with a brush dipped into carbon dust.
I rendered this monkey skull drawing at a Smithsonian scientific illustration workshop in Highlands, NC. I can do better with models that hold still. I admire the skill of some artists who can render a drawing on the fly, but I’m too slow for that. I keep this drawing to remind myself of that delightful week of constant learning.
Knitting, writing and other joys 
The man from the Smithsonian who taught the scientific illustration classes where I encountered carbon-dust rendering said that it is a very old technique in that field. They use it to get the same effect as a black and white photo (continuous tone) look. We used mylar drawing “paper” that had a bit of a tooth to catch the dust although it felt smooth. It looked and felt like a good tracing velum. After we refined our sketch on other paper, we laid the mylar over the sketch. Then we rubbed a fine-grain charcoal pencil on fine sandpaper so the dust fell in a saucer and picked it up with a small, flat, stiff-bristle brush that we’d trimmed at an angle with a point at one edge. Using paper towel to remove extra dust from the brush, we built up the carbon dust on the drawing little bit by little bit. Where we needed sharp lines, we used a fine carbon pencil. Where we needed a white mark or dot, we made a point on a kneaded eraser and touched it to the drawing. When it was finished, we mounted the mylar over white paper. I think it has a fixative on it but don’t recall. To find better instructions than this, I’d look for an old book on scientific illustration techniques. You might also ask someone at the Smithsonian for a reference. Since you do watercolor paintings, I imagine you could do this technique with more ease than I did. I’m not accustomed to working with a brush.
I came across your blog while doing a google search on the carbon dust technique. I am very much interested in this technique and was wondering if you could share some tips on this technique or if there is a book I can locate to read up on it.
Any help you can give will be greatly appreciated.