 three purposes: to mix paint on your palette before 
applying it, to apply paint (as an alternative to using a brush), and to scrape 
off your palette when you are finished painting. The latter use is probably the 
only one that pretty much requires a knife, or some sort of scraping device. A 
long flat knife is best for this. Using a knife for mixing colors is not 
strictly necessary, as you can do this with a brush as well. But it is easier to 
wipe off a knife, and therefore easier to mix clean co