Updated on 19 February 2017 (Harvard referencing).
6 March, 2016. I am not sure why, but I found it very hard to make sense of the instructions to this exercise. Looking at the respective work of some of my student colleagues did not help either: In both paintings the ground can be a wash and in both I paint over that with a predominantly opaque layer. In both sheets, opaque and transparent paint need to work together. The only difference I can see is that in one case it is the background, which remains transparent if I choose this approach, in the other it is the tree. In particular I am unsure what to make of the sentences “Mix up a light grey and apply this to the shapes formed by branches … Modulate this grey as you move away … “. I guess that this instruction is meant to apply to both paintings, but if I paint over either the positive or negative representation of the tree, it will mean to cover up the only real difference between the two. Since I understood the goal of this exercise to compare opaque and transparent approaches to painting a tree, I decided to – for the moment – ignore the above instruction and wait for tutor feedback. I got ready choosing two sheets of acrylic paper and mixing a dark wintery colour by combining primary magenta, gold ochre and bluegreen, with white or water to be added where required.
7 March, 2016. Finished the two paintings today, having decided to paint the apricot tree in our garden, which is getting ready to grow its buds.
Here are the results. On top is the “positive” tree, which I decided to paint with relative coarse brush strokes on top of the light grey opaque ground in order to make visible the bark characteristic of this species (Fig. 1).

The dark wash prepared for the second part of the exercise I had to produce in two layers, otherwise it would not have been dark enough to compare to the solid colour in the first painting. I quite liked the brush strokes and decided to set them diagonally in order to emphasize the relative direction of growth of the tree (Fig. 2). Despite the help of charcoal it was not easy to reproduce the negative spaces correctly and I had to literally talk myself through the exercise. In a few places I painted over a twig, but most of it seems more or less correct.

I am unhappy with both paintings for the coarse approach to the subject, but again it may have been me misinterpreting the instructions.
Asked to assess the strengths and limitations of each technique I would – cautiously – assume that painting a positive object on a prepared ground will produce a more realistic feeling of space (object in front of background). The greater transparency of a background wash will most likely produce a more credible feeling of air, while a completely opaque background will suggest a dull day, probably in stifling weather. Also, I found that an object as complex as a tree is by far easier to paint positively. However, I like the effect produced by painting the negative spaces better. Probably due to my lack of practice in doing so the tree is more alive and seems to physically make contact with the air surrounding it. Since both paintings are silhouettes only, I am so far not able to compare the respective strengths of the two approaches regarding credible representations of trees.
What I also learned in this exercise was to be wary using acrylic paper. The “professional” paper I had bought rolls up in the most unfashionable way and is almost impossible to reshape. I had therefore to place a glass plate over the sheets in order to take the required photos and unfortunately could not get rid of all the reflections. Also, the colour is not quite correct and the brush strokes are hard to see. I will retake the photos if I am instructed to have another go at this exercise.