On this same subject of negative painting I came across this photograph taken last year when I was preparing for an Autumn colours workshop. It's a good example of how the technique keeps coming up no matter what your painting subject matter.
(You can click on the image to enlarge it.)
Using the collection of leaves in front of me as inspiration for colour and shape, I have laid a first wash bottom right.
I've used a variety of colours as in the real leaves and have dropped them randomly on to wet paper. I've made sure to leave an interesting broken edge around the outside of my vignette to represent leaf edges.
You can see the drawn pencil lines underneath the wash and now I'm about to paint around and between those pencil lines with darker washes of the same colours in order to achieve the finished effect in the Autumn Leaves painting on the left.
Once I've painted the spaces in between the leaves, I will allow this to dry and then go into this wash again to find more negative shapes to represent more leaves underneath.
So another example of negative painting in use.