Home Online catalogues True to Nature. Open-air Painting 1780-1870 105. Pierre-Henri de Valenciennes Toulouse 1750 – 1819 Paris Study of Clouds over the Roman Campagna, c. 1782-1785 In his treatise Élémens de perspective, Valenciennes recommended that painters begin with the sky when making open-air oil sketches, as it is the main source of light in nature and sets the overall tone of a landscape. This quickly painted cloud study is part of a group executed by the artist during his second Italian journey of c. 1782-85. Working from an elevated position, he summarily indicated the rolling hills of the Roman countryside and focused his attention on the sky, capturing the everchanging silvery-white cloud formations with a lively impasto. Because of the ephemeral quality of atmospheric phenomena and weather conditions, Valenciennes advised his readers and students to spend no longer than two hours on a sketch, with particularly fleeting effects such as sunrises or sunsets limited to half an hour.