Painting rusty objects in watercolours involves four particular techniques:- wet on wet, splash painting, drip painting and glazing. For the classes, I sorted out some old rusty nails and tools. I asked all learners to set up their own composition. We made contour line drawings of the objects.  

There is a wide variety of colours that appear on rust, depending on how the rust was formed and where. The rusty nails palette: yellow ochre, light red and a range of browns from light to dark. Each one of these small objects can be painted wet on wet. Wet the area of the nail and apply a light wash of yellow. Add the other colours from light to dark as the paper is drying. Angle your board if you want any of the paint to run, which works very well with the idea of rust, as you see then a further design principle, movement. Once all the nails are painted (using the same technique, but varying the tones of the colours slightly) we then moved on to the larger objects, with not much change to the formula used for the nails. The key is to work light to dark, on damp paper as much as possible.  

Blue and rust make very good palette partners. For the background I mixed my own blue using cerulean and ultramarine. I worked in sections, wetting the top left hand corner of my paper first. I covered the painted nails with tissue and applied a blue wash to the background. I then splash painted on various colours of brown, using different size brushes. As the paper is drying the subsequent splashes will dry a darker tone, as there is less water mixing in from the wash on the paper.  

When the painting was 100% dry I added stronger tones of the final colours on the objects (glazing).

To add some drip painting, when you apply your splashes, angle the board, so the paint moves in the direction you want the rust to move in. With this particular subject, the background becomes a key part of the composition. Add shadows to one side of the objects, as this is a flattish composition they add more 3D effect. For the shadows I used chromatic black and a purple mix.