In researching my own workshop instruction methods, I have found some You Tube Vids that I like. Here is Kitty Wallis, of Wallis paper fame, and she is explaining the properties of not only her unique ground, but the usage of liquid pigment and its benefits. I use this method to either wash a tone on my ground, or to actually get down an underpainting with some detail. I am planning one for a barn image now, where the overwhelming presence of the Earth's color is going to be too much for the painting. If I underpaint a good color, though, I'll be free to continue without worry.