1. Cut a window mat to fit the artwork. Note: Smooth alpha-cellulose boards work the best.
2. Using a corner gauge mark out the positions of your lines and washes using a pin.
3. Draw light lines in pencil either side of the panel where the wash will be.
4. Mix the wash from artists' watercolours and water to the desired colour.
5. Align a ruler or staight edge with the outer pencil lines and supported above the surface of the mat by 10 - 15mm. The ruler can rest on two blocks of wood to raise it to the required height.
6. Using a flat sable brush, close in size to the width of the panel, paint the panel with clean water by running the ferrule along the straight edge. Try to avoid wetting outside the pencil lines.
7. Leave the board for a moment until the water wash has just soaked in.
8. Charge the flat sable brush with the coloured wash and paint the panel as in stage 5 & 6, starting in the top left hand corner of the mat. Try to work quickly and do not wait for the brush to run out of paint before reloading it. When you reload the brush you must start on the panel again picking up the puddle of colour left behind when you removed the brush.
9. Leave the completed wash to dry before applying the lines as explained previously.
It is better to paint the wash paler than required because another wash can always be applied to strengthen the colour.