The 1870s saw the peak of Impressionism, both ads a coherent group movement and as a painting style. During that decade, artists divided their time between landscape painting and studies of Parisian life. The gentle rural landscape along the Seine valley between Paris and Normandy formed the main source of inspiration for Monet, Sisley and Pissarro. Renoir, who regularly worked beside Monet during the first half of the decade, also painted many scenes of interiors, figures and city subjects. Monet and Renoir were joined in Argenteuil by Manet in 1874. In Manet's oil paintings of this period, figures, as usual, dominated even his outdoor scenes, although he lightened and brightened his palette at this time. During the decade, Degas and Manet continued their em­phasis of the 1860s, painting mainly themes of modern Parisian life, such as the boulevards, cafe scenes, the Opera and the ballet. Gustave Caillebotte (1848-1894) split his allegiance between city life and landscape. The earliest works in the Impressionist style by Mary Cas­satt (1845-1926) date from the latter part of the decade, and her subjects included the Opera, indoor and outdoor figure scenes. She often chose themes comparable to those of Berthe Morisot (1841-1895), but their style and handling were quite individual. Pissarro and Cezanne often worked on landscapes together during this period, although Cezanne divided his time between the north and his native Provence.

By the mid 1870s, the artists' period of apprenticeship was over and their ideas, aims and differences firmly established as a result of regular discussions at Paris cafes from the latter half of the 1860s onwards. Indeed, by this time the Impressionists - or independents as they were still called in the early part of the decade - found themselves, with the exception of Manet, sufficiently united in their disagree­ment with the academic system and its outlet, the Salon exhibitions, to present a united opposition to those institutions. Although their first discussions on the subject in the mid 1860s had come to nothing. by 1874 the members of the Impressionist group finally established their own alternative exhibitions, independent of the official Salon. Their first show took place in April and May 1874, when a critic coined the term 'Impressionist'.

Basic methods of Impressionism

The brilliant young French Symbolist poet, Jules Laforgue (1860-1887), gave a perceptive and informed description of the Impressionist approach, in an article written in 1883. He said the Impressionist artist was one, who 'forgetting the pictures amassed through centuries in museums, forgetting his optical art school training - line, perspective, color - by dint of living and seeing frankly and primitively in the bright open air. . . . outside his poorly lit studio - has succeeded in remaking for himself a natural eye, and in seeing naturally and painting as simply as he sees.' In seeking to free themselves from the conventional studio vision of line, space and chiaroscuro, the Impressionist painters had to re-educate their eyes by careful observation of natural outdoor light effects. They had to learn not to see landscape through the artificial eye of European oil painting.

Photography gave them one alternative vision of the natural world which was not based on painting, and Japanese prints provided another artistic option. The Impressionists' friend and patron Theodore Duret. politician and art critic. noted in an important essay in1878 'Before Japan it was impossible; the painter always lied. Nature with its frank colors was in plain sight, yet no one ever saw anything on canvas but attenuated colors, drowning in a general halftone.' With their 'piercing colors placed side by side', Japanese artists showed 'new methods for reproducing certain effects of nature which had been neglected or considered impossible to render'.

Duret summarized 'After the Impressionists had taken from their immediate predecessors in the French school their forthright manner of oil painting out of doors from the first impression with vigorous brushwork, and had grasped the bold, new methods of Japanese colouring, they set off from these acquisitions to develop their own originality and to abandon themselves to their personal sensations.'

While their older colleagues, Manet and Degas, remained essentially committed to studio working methods. albeit novel ones, the younger artists. Monet, Renoir, Pissarro, Morisot, Sisley and Cezanne, used outdoor landscape studies as the vehicle for their research into new ways of painting the real world. They abandoned the strongly contrasting lights and darks of Romantic and Realist oil painting. In particular they rejected the use of the sombre earth colours, browns and blacks, which dominated the palettes even of artists like Manet and Degas in the 1860s. Instead they explored the pale colours and close tonal values of studies by Corot (1796-1875), the luminous skies of outdoor seascapes by Boudin (1824-1898), and even the pale opaque shadows which helped flatten pictorial space in works by Ingres (1780-1867). They began to exploit more fully the light-enhancing properties of pale commercial primings, and gradually replaced the traditional brown ebauche with a brightly coloured initial laying in of paint which related directly to the final colors of the oil painting. They continued and extended the making of outdoor etudes, adopting this freely executed study stage as their finished work.

Supports

Although the smooth, dark surface of mahogany panels was often used to advantage by earlier nineteenth century landscapists, the Impressionists preferred the lively give and texture of woven fabric supports. Prepared paper and card were often also used as supports for oil sketching in this period for reasons of economy and their light weight which made them easy to carry. Canvas is a coarse cloth woven usually from flax or cotton. but sometimes from hemp. Its widespread use as a painting support dates from the Italian Renaissance. The rise in importance of fabric supports coincides with the increasing cultivation of flax in Europe from the middle Ages on. It remained the most important vegetable textile fiber in Europe until the end of the eighteenth century, when cotton began to be imported on a large scale from the United States.

Canvas was first used in easel painting merely to provide an underkey for the gesso grounds of medieval panel oil paintings, and only emerged slowly as an independent oil painting support. The adoption of canvas went and in hand with the development of oil painting. Its textured surface stimulated experiments, especially among the Venetian artists, in expressive brush and oil paint handling, which produced emotive effects impossible to obtain with fast drying egg tempera colors on smoothly primed. Rigid panel supports.

By the early nineteenth century. Ready made canvases were being sold in France in a standardized range of sizes for easel painting. The range then available. in a squarish rectangular format designed for portrait and figure work. spanned from a small (No 3) canvas, measuring approximately 6in (15.5cm) by 8in (20.8cm). to the largest. (No 120), measuring approximately 6 feet (1.9 metres) by 4 feet (1.2 metres). At that time the metric scale had not yet been fully established. In the early 1830s a longer 'landscape' format was introduced, together with an even more elongated 'marine' shape. By the 1880s five series were on the market. These were the original portrait. vertical landscape, horizontal landscape, vertical marine, and horizontal marine series. Within these five series, each format number had the same sized shorter side, only the longer side varied in length. The code-numbering of portrait formats probably had its origin in the seventeenth century when the major art theorist Roger de Piles recorded that canvas pieces were sold according to cost - a 'canvas of 20 sous' was of given, commonly accepted dimensions. Thus, for example, a canvas costing 20 sous became canvas size No 20.

Despite the fact that most artists and writers thought that the dimensions of standard formats had been rationally conceived to conform with some aesthetic, harmonious ratio, such as the influential 5:8 proportions of the Golden Section. they were in fact determined purely by economic factors. In order to be able to prepare stretched canvases and picture frames in advance. color merchants found it expedient to use fixed measurements, rather than having to follow the whims of artists by making numerous sizes to order.

Before mechanization in the weaving industry hand-loom widths for canvas depended upon the distance a shuttle could be thrown through the warp by the weaver. In France this was commonly around 1 metre (3 feet) up to a maximum of 1 metre 40cm (4ft 6in). When standardized sizes are analyzed in relation to the canvas widths available, it is clear that the formats chosen were those which could be cut most economically from the fabric, avoiding undue wastage. For large-scale oil paintings, like those of historic subjects often shown at the important, annual Salon exhibitions, artists had to order specially made canvases, which were sewn from strips of fabric.

The mechanical spinning and weaving of linen was about 50 years behind developments in the mechanization of the cotton industry, so entirely machine-made linen canvas was not common before the mid nineteenth century. Although large, unbroken widths of canvas made massive pictures simpler as the century progressed the tendency was, on the contrary, to smaller, easel-scale oil paintings. This development was prompted by two chief factors the demands of outdoor oil painting which made very large canvases unmanageable, and the necessity for artists to produce many, smaller oil paintings to satisfy the new middle-class market, which called for reasonably priced artworks which would fit in small city apartments.

Most nineteenth century artists used standardized canvases for their easel-scale works, but the Impressionists and those who followed them found new more appropriate ways of exploiting them. Thus the commercial availability of a product had a direct impact on the most basic level of artistic creation - the initial selection of canvas shape on which to start work. This inevitably influenced compositional design, as this must relate to the canvas edges and overall shape. So an artist planning to tackle a particular subject must choose the most suitable canvas proportions to enhance the projected design. The positioning of the subject on the chosen canvas size and shape is called mise en page, and is a crucial, though underestimated, determining factor in Impressionist painting. It shows how self-conscious these artists were, contrary to the currently popular myth of their naive spontaneity.

Non-standard supports

Although the majority of their artworks are on standardized canvases, the Impressionists did not adopt them wholesale. They also experimented with unusual canvas shapes, either to suit particular subjects or to complement innovatory compositions. These would have been made up to order, usually with ready primed canvas. Monet and Degas were among the artists most overtly and consistently experi­menting with novel formats and compositions. For example, certain of Monet's studies from the early 1870s of Dutch land- and seascapes, were executed on canvases selected in advance to complement the low-lying panoramic scenery of Holland. These were made-to-order canvases more elongated in shape than even the longest commercial 'marine' format. Artists were also beginning to explore the potential of completely square canvases.

Monet and Degas both began using square canvases in the latter 18 70s, and Pissarro then Gauguin followed soon after. Because of the symmetry of their sides, square canvases accentuate an appearance of flatness, making it difficult to create the illusion of reality which a rectangular format can more readily suggest. Therefore square formats were avoided by conservative artists, while they presented the independent painters with an exciting challenge. On square canvases they could more readily wrestle with the problems of compositions in which a balance is created between the illusion of depth and a simultaneous stress on flat surface design.

Commercial priming was done on large expanses of canvas, which were later cut down to the standard sizes and tacked onto their respective stretchers. It is thus possible to identify commercial preparations by examining the canvas edge, as the priming goes right round to the back of the stretcher. Where canvases are primed by hand after stretching, only the face side is covered, and raw canvas remains visible on the overturned edges and around the back.

For priming, the canvas was tacked to huge wooden frames in the workshop and balanced on trestles; the canvas was then primed horizontal. Using tools, like the priming blade which dates back well before the seventeenth century, the first layer of glue size was applied to the fabric. Two skilled men, one either side the flat of canvas, picked up the preparation in ladles and spread it thinly with the blades, working back and forth from the middle out. The size layer sealed the pores of the canvas and made it less absorbent, and therefore less vulnerable to the corrosive effects of the oxides present in the oil of the ground - the next layer. The size dried preventing undue movement in the fabric threads. The surface was then rubbed lightly with a pumice stone to remove fuzz and protruding irregularities in the weave.

Then the ground coats, one or two layers of opaque color bound with oil, were applied with the priming blade, ideally allowing thorough drying time between coats. One of the hazards of off-the-peg ready primed supports was that artists had no means of telling when the canvas had been primed, and if it had been left long enough to dry thoroughly. Cracking all over the paint layer could result from a ground which continued to dry long after it had been painted on. Despite this danger, it was rare for artists to take the trouble to prepare their own canvases. As oil grounds could take a year or more to dry, artists were often advised to store them before use to make sure they had a sound base on which to work.