I think this negative painting effect is born of working from photographs a lot. It aims for realism and has little to do with conceptual art or spontaneous expression and as such wont be everyone's cup of tea! I'm trying to capture a realistic sense of depth and 3D. So that, like in a photograph, you feel as if you are travelling into the painting.
Many people find this concept of painting back to front difficult to grasp. So if this is the case perhaps having a go at this demo stage by stage will make the difference.
First I made an outline drawing of leaves overlapping each other. These might be clematis leaves.
In this first stage of painting I laid a wet in wet wash. I had mixed up some yellow and some blue separately in my palette and also mixed a green by combining the yellow and blue. I wetted the whole of the paper and the dropped in yellows and greens wet in wet. I made sure the yellows went over the uppermost leaves and the darker greens went into the areas between the leaves. This started the 3D effect straight away as the yellows stand out and the greens recede. I ignored the pencil lines at this stage, just wanting to get a general effect to start with.
I let this dry completely. It 's important to allow each stage to dry completely...you can use a hair dryer!
Before painting here, you see I have drawn in some stalks in the middle depths as a guide for my painting. With a darker green (with more blue mixed in with the yellow) I painted AROUND just the uppermost leaves. Where one leaf overlaps another, I brought the darker paint underneath the top leaf to make it seem as though a shadow was being cast on the lower leaf. You can see I have painted over the underneath stalks and leaves at this stage. I let this dry completely.
Then with an even darker green I painted AROUND the underneath leaves which as a result were now standing out but were darker in tone than the very top leaves. At the same time I used this darker green mix to paint each side of the leaf stalks and tendrils that I had drawn in the middle depths, thus making another layer of depth. Once again I let this dry.
Finally I painted in some more veins on the leaves which introduces depth and form within the leaves. So the leaves themselves become 3D. I deepened the shadows cast by the overlapping leaves by going over with a fairly watery bluey green. And I was pleased with my 3D effect!
And finally here's this 3D technique used in one of my paintings. This shows a section of a clematis painting where I have used the negative painting method to portray the leaves.