The Difference Between Watercolor and Gouache Paints
jetpens.com
jetpens.com
I draw with vine charcoal, smudge and adjust, then wash it on canvas with a brush dipped in water, it makes a nice watercolour style effect. I suppose it’s more like gouache after reading this.
I started experimenting with compressed charcoal crayons too. I dip them in water then rub directly into canvas. It gives a very strong black which is perfect for accents and dark surfaces.
Never tried the process your describing. I'll try watercolor paper first, and then canvas - I assume you mean a primed / gessoed canvas?
Canvas isn’t a particularly good surface for charcoal, but I like having a very large work area