I have been doing palette knife painting regularly for the past few months. Some things that I learnt:
1) Use knives that are sturdy and do not 'bend' with the pressure.
2) Have a variety of shapes, from the broad spatula kinds to pointed, sharp edged ones.
3) Use broad spatulas to do surfaces like skies, walls and backgrounds and use the sharper ones to do finer details.
4) Palette knives are better for Alla Prima and impressionist works. Keep in mind that the approach that you use in a regular layer to layer painting cannot be adopted here. e.g. If you want to highlight lemon yellow or auburn streaks in the sky, it's best to do the streaks on the blank canvas, because as the paint is impasto, if you plan to do the streaks after applying blue for the sky, the yellow/auburn will blend with the blue, thus making it impossible to show up on the sky. This will restrict the effect of the sky. I recently did a scenery where I wanted to highlight autumn leaves on the greens of the trees, but failed to do so as I had already applied the greens. The lighter colour just blended into the greens and disappeared.
5) Do not use colour sparingly. Pile on. The very fact you are using the knife is for an impasto effect. Knife work doesn't have to look photo finished. It should have a painterly touch to it, and the advantage of the bright, unadulterated colours ( no medium) should be felt. The colours should 'shout out' from the painting!
6) Plastic knives are handy and are great for small paintings, especially when you have to build in details for flower petals, eyebrows, eyes, parts of houses etc etc. However, for very large bases, you wouldn't want to use them, as they bend with pressure and may tend to alter the shape of the strokes.
7) Steel knives are the best. However, make sure they are stainless steel as otherwise, they will rust in no time.
8) When using knives, first make the values on the palette and pile on paint straight from there on to the canvas. Please do not make the mistake of using a medium, as the colour runs on the canvas in that case and it will give a 'dripping' look to your painting.
9) You can adopt a top to bottom approach while painting, as that does not get you into a mess of colours. If you start working from the top of the painting and proceed till the bottom, there is lesser chance of colours sticking to your hands and elbows! This is easier said than done however and will come with practice!the paint being thick and wet, gets off the canvas at the slightest pretext and if you aren't careful, you will be a colourfull mess in no time!
10) You can also adopt a brush and pallete mixed work, if you want to give some work a 3d effect, with the palette knife and the rest of the background done in brushwork.
11) While doing figures and portraits, you can adopt an alla prima technique to block values . I find the thin plastic knives great for this. The plastic knives are also great for plein air.
12) You need to finish the painting at a go, as blending of colours becomes difficult if the paint begins to dry since impasto paint will be patchy when it dries. The painting will take at least three weeks to dry completely.
13) If you are planning to use knives for plein air, its best to use acryllic and not oils as they dry faster, unless, you have provisions of getting them home or to the studio untouched.
Photos of two of my knife works.
14) Keep 2 or three clean rags and some rolls of tissue as each time you apply paint of different colours you have to wipe. You can use different knives for different colours/ values also.
15) Always, always wear an apron.
16) Put your signature after the work dries.
I've been having lots of fun with the knives. Hope you do too!
Here's the song cuts like a knife, by Bryan Adams, dedicated to this post:
http://youtu.be/6VZhSkREYBc
