Quiz: 
What was the pigment Indian Yellow, which stopped being available (in that form) in the 
early 20th Century, made of?

Answer: 
The urine of cows that fed only on mango leaves.

Edges: 
Many painters don't make use of their brush edges...especially to their advantage. 
Every painting should incorporate different edges.....distant objects might need to be 
blurry, while your focal point may need to be sharp and crisp. Below are 3 ideas for 
brush edges.

Hard Edge:...
Most edges used are when one color comes up to and stops right next to another                       
color. This is what a lot of painters use, even if not appropriate. 

Soft Edge:...
Mixed: The edge of one color is wet and is mixed into the next edge color that is also 
wet. This makes blending graduation of  the two colors.

Optical:...
This edge makes the eye blend or causes the painting to have a unity because the 
underpainting pops up throughout the overall painting. Paint up to a color edge, but not 
right next to each other, leaving a space between the 2 edges. The underpainting shows 
in between. 

Readings: 
Check out the book, Painting Shapes and Edges, by Hazel Harrison.
I'm a true believer that if you carefully observe the shapes in your painting 
(starting with the main shapes, then breaking them  down to the smaller shapes) 
anyone can paint or draw anything. This book supports and explains that theory.