Too much medium: slippery, weak paint
“My brush is just sliding around on the canvas and the paint will not stick or cover anything.”
What is happening
The paint feels overly slick, greasy, and uncontrollable on the canvas. Instead of laying down rich opaque marks, the brush pushes translucent, runny puddles that slip off edges.
Adding too much oil or medium over-dilutes the pigment particles and breaks down paint body. The pigment separates from the binder, leaving insufficient friction for the brush hairs to deposit colour evenly.
The 30-second test
Dip a brush into your mix and touch the canvas; if paint pools instantly around the stroke edges leaving a transparent center, you have drowned the pigment.
How to fix it
- Blot away the excess slippery medium from the canvas using a lint-free cotton rag.
- Scrape slippery pools off your palette with a palette knife.
- Squeeze fresh paint directly from the tube and introduce medium only in tiny, controlled drops.
- Re-apply the paint with firm, deliberate brushstrokes, letting the natural pigment body grip the canvas.
Can it be saved? Rescue
Wipe off the slippery, pooled paint with a clean rag and repaint using paint straight from the tube.
Drill: Medium calibration drops
About 15 minutes. You need:
- Oil palette
- Tube colour
- Linseed oil
- Palette knife
Place three identical mounds of paint. Add zero drops of oil to the first, one drop to the second, and six drops to the third. Compare body and brush resistance.
Background reading
General teaching sites on this subject. They are a reading list, not page-level citations for this advice.
The advice is a generated synthesis of common teaching practice and has not been checked line by line against any source; treat times and difficulty as estimates.