UNDERSTAND THE TECHNIQUE
Tip and belly do different jobs
The tip makes a fine contact. Farther back, the head has more volume and can carry more paint. With the brush held consistently, a gentle increase in pressure can bring more fibres onto the surface and widen the stroke. The round brush is therefore not just a tool for small details. Larger versions can make both flowing lines and continuous shapes of colour. The Fleury film describes thick and fine lines, blending and the water capacity of larger round brushes. Test how your own stroke behaves with the same paint on a spare piece.
Check the paint load before the stroke
Distribute paint through the head without pushing it into the ferrule. Shape the damp head gently and make a test stroke. If it starts with a puddle, remove excess liquid. If the line immediately becomes dry and broken, the mixture needs better flow or the head needs more paint. With watercolour in particular, consider the surface and loading together: wet paper responds differently from dry paper, even with the same brush.
Thin, broad and thin again
Begin with light pressure, moving your hand as soon as the brush touches down. Increase the pressure gently during the stroke without sharply bending the head. Towards the end, lift the head while continuing forward. If you stop first and lift afterwards, you are more likely to leave a heavy ending. Practise the movement in different directions. Turn the paper if a direction feels unnatural. This lets you learn the movement independently of a finished subject.
Pressure changes become leaves and contours
A stroke with a narrow beginning, broader middle and fine ending can serve as a simple leaf shape. Two gently curved strokes can create a wider leaf. Add a stem or vein later with a finer tip. Apply the same movement to fabric folds, curls or organic contours. Not every line has to be equally wide. A deliberate change can make a shape more lively. Plan where the line should widen rather than changing pressure at random.
Find the right size
A small version is often enough for a small accent. For longer, fluid strokes, a larger head may be more comfortable, even if the line begins finely with its tip. Compare actual millimetre measurements and your stroke test. The largest size is not automatically right: on a small painting, its paint quantity may be hard to control. Choose the brush that lets you create the required shape in one steady movement.
All sketches show shape and movement direction schematically. The actual paint mark also depends on paint, surface and moisture.