some talk about drawing lines with a skinny brush
If I want to draw skinny lines with paint, first I mix drops of turp into the paint with my palette knife until the paint flows off the brush. But not too much turp or the pigment will be too diluted.
Here’s the easy way to paint skinny lines : Scoop up the runny paint with the palette knife. Hold the palette knife with one hand and the paint brush with the other hand while you stand at the easel. Then you don’t have to keep reaching back to your palette and mixing in the turp. You only have to move the brush a few inches back to reload paint which is already the right consistency. Then you can scribble away with the little brush much easier.
Sisterhood of the Muse 