The palette knife is more than just a tool for mixing paint. (duh!) It can be used to apply your paint as well. (duh again!) Some painters use a knife exclusively, and some painters (like myself) prefer to use a knife in conjunction with other brush work.
But if you do use a knife and brush together, how do you integrate the different kind of mark each tool leaves behind? Both have a different look and feel, and often, if nothing else is done, the two marks don’t seem integrate. They fight each other.
Here’s a little-known secret many folks don’t know: Painters of old often laid down thick gooey passages of paint with a knife on top of a more thinly brushed area, and then came back to work the thick goo with a stiff clean brush! They integrated the flat edginess of their knife work into the brush work below. A few judicious strokes with brush around the knife-work, and voila! Juicy impasto which looks like it belongs with the rest of the painting! As if it was casually thrown down by a skillful painter!
You can also use the brush to shape (or correct) your knife work after the fact. But keep in mind, you only get a couple of attempts to correct a passage before the area must be scraped down and built up again. There is still some skill involved.
And for the Palette-Knife Purist out there, please don’t take this post the wrong way. I salute you! I appreciate a good palette knife painting as much as anyone else does. But to integrate one’s knife work into the rest of our stroke-making expands the artistic toolbox. It also increases our poetic vocabulary and vision.