The Liner Brush
There are many kind of liner brushes. For this demo I used a #2 Aquafine Daler and Rowney Script Liner. I also frequently use Princeton Select Liners.
Liner Brush Exercise:
Reference Photo #1. Notice the tree does not overlap other trees.
Reference Photo #2: Notice in this reference photo that foreground trees overlap background trees. Always paint from background to foreground.
Here you can open and Print it out:
Exercise #3: Tree with Ivy
You can open this pdf file and print it out: