With Van Gogh it was rarely a question of adorning a letter purely for the fun of it.9191. Exceptions are a few small drawings in letters written before 1880, such as 32, 39 and 99. In his case the sketches basically served one purpose, which was to give the recipient an idea of something that he was working on or had finished. Another factor at the beginning of his career was to show Theo how he was progressing. In Etten in September 1881 he sent him a letter with 12 of these sketches, some of them in colour.9292. Letter 172. They were meant to convince his brother of his commitment and of the fact that he was choosing subjects that he idealized: labourers and peasants at work. He added: ‘A change has come about in my drawing, both in my manner of doing it and in the result’. And that is what he wanted to demonstrate with his letter sketches. He admitted in this letter that the proportions were not always correct, and some of the sketches are almost primitive, but he worked up the one of the man with his head in his hands with colour. It was based on a drawing that he considered one of the best that he had made so far.9393. The drawing is Worn out (F 863 / JH 34).

The sketches in letters to fellow artists are part of the exchange of ideas on paper, giving an idea of the sort of subjects he was tackling. Here, too, he tailored them to the recipient, and sometimes this was done to show off his skill. This is why now and then he sent a quite highly worked-up sketch with a letter, some of which are now catalogued as drawings in their own right, such as Old man with an umbrella seen from the back (F - / JH 214), which was simply drawn on a page of the letter.9494. See letter 268. The sketch of a woman’s head that opens letter 505 to Theo, which Van Gogh again calls a ‘croquis’, was done with more than his usual care.

Although some were more highly finished than others, the letter sketches cannot be regarded as a stage in the creative process. At most they are a reflection of one, and as such are not part of his purely artistic oeuvre. The value of the sketches lies in the fact that they forced him to depict the essence of a drawing or painting. He usually drew them with ordinary writing ink, and in some cases he added colour notations, which can be compared to the actual paintings, such as the Small pear tree in blossom, after which he made a sketch in letter 597. A few of the sketches are even additions to the oeuvre in that they depict an earlier version of a work or one that has since been lost. This applies particularly to the Dutch period,9595. See, for example, the sketches in letters 265, 400 and 435. but for example there is a sketch in letter 693 to Eugène Boch after a painting of the public garden in front of his house in Arles that is no longer known.

A clear line of development can be traced in the letter sketches that was directly due to the amazingly rapid development of what Van Gogh called his ‘draughtsman’s fist’. While the early sketches are rather dark and densely worked, the later ones are more airy. No matter how small they sometimes are, Van Gogh gradually used his pen in a more varied way, and the results look less heavy that in his early years. Initially he concentrated more on surfaces and the effects of light and shade, but later he gave freer rein to the line. This can be illustrated by comparing the sketches of countryside scenes in Drenthe in the letter written to Theo around 22 October 1883 and the sketches made in Les-Saintes-Maries-de-la-Mer in June 1888 in a letter to Bernard.9696. Letters 398 and 622 respectively.

There are a couple of dozen sketches which are not related at all to works by Van Gogh, but they are at least as important. They are small drawings illustrating the materials he worked with or the conditions under which he was working. They range from sketches of his studio to show how he had ordered shutters for the windows to control the fall of light, how he used his perspective frame on the beach, or how he envisaged the arrangement of a triptych,9797. Letters 318, 253, 597 and 776 respectively. to a description of the colours on his palette, the thickness of his Faber pencil, the shapes of a scraper, a point and a piece of natural chalk, and the width of his brushes.9898. Letters 253, 354, 325 and 777 respectively. Publications on Van Gogh’s studio practice in his final years all refer to these little sketches, which shows how informative they are, supplemented with the many written passages that Van Gogh devotes to his materials, whether it is his enthusiasm for the properties of lithographic crayon, the possibility of fixing drawings with milk, the quality of the colours made by père Tanguy, or an order for paints that he sent to Theo.