This section will be on shading. And assuming you have done all of the work up to this point and really learned the lessons things will start to come together now. The shading you will be learning will let you really start to show form and volume. So this section should be a lot of fun.
For this section like the perspective section we will have to use some supplemental materials. As always I will supply a list of free ones and then also some you can buy.
Free materials
Light and shade : with chapters on charcoal, pencil, and brush drawing (c1897)
Guptill, Arthur Leighton,1922. Sketching and Rendering in Pencil.
The Guild Handbook of Scientific Illustration – This book is not free but the preview chapter on light and form are very helpful.
I will expand this free section myself when I get time to make some examples and write some basic tutorials.
Materials you can buy or rent.
The best thing I have found to learn shading with are the DVDs by Scott Robertson. He has 3 DVDs on rendering matte surfaces. You can buy them here thegnomonworkshop.com or rent at least one I know of at Smartflix.com