produce oil sketches as independent works was Giovanni Benedetto Castiglione, an amazingly fecund generator of compositions on a relatively small range of subjects. He grew up and trained in Genoa, and apparently had contact with both Rubens and Van Dyck during their stays there. He produced a large number of small works, mostly on paper, in a mixture of mediums - drawings or gouaches finished in oil, oils with pen details - in fact, most possible permutations. Detail is typically restricted to a few key points, with much of the subject conveyed in impressionistic fashion. By this time a collectors' market for studies in drawing was well developed, and there was appreciation of their energy and freedom. Castiglione's sketches to some extent seem to trade off this appreciation, and look more unfinished and offhand than they actually are - a concept with a great future. A systematic producer of small modelli sketches on canvas with a high degree of finish was the 18th century Venetian Giovanni Battista Tiepolo, whose superb technique is often shown at its best in reducing a huge altarpiece to a lively but precise rendering at this small scale. At roughly the same time Jean Fragonard was producing a series of virtuosic Figures de fantaisie, half-length portraits of imaginary subjects, purporting to have been painted in an hour. By the 19th century oil sketches, often referred to as "oil studies" if from this period, had become very common, both as preparatory works, and for their own sake. The popularity of the oil sketch engendered the need to formulate distinctions. The esquisse, or oil sketch, tended to be inspirational or imaginative, often originating in literature or art; the etude, or study, tended to represent an observation of nature, painted from life. In academic painting the oil sketch took the form of the croquis, a small and gestural compositional study, and the ébauche, a dynamic laying-in of paint on the full-scale canvas, a temporary stage of the painting eventually leading to greater elaboration. John Constable made extensive use of sketches for his landscapes, both of intimate scale, often in a sketchbook on paper, and in full-scale sketches for his largest "six-footers", which he used to refine his compositions. Delacroix, Géricault, Manet and Degas are other artists who often used them. For some oil sketches Degas painted in essence, a technique by which the oil had been all but removed