An exhibition showing off colourful open-air artworks by major Impressionist painters such as Vincent van Gogh and Claude Monet is set to open its doors in Madrid on Tuesday. The \"Impressionism and Open-Air Painting\" show at the Thyssen-Bornemisza museum features 113 works and explores the evolution of outdoor painting -- an art-form perceived as having transformed the world of painting during the 19th century as Impressionists took it to its apex. Previously, artists had commonly produced landscape paintings indoors by using sketches. The exhibition took about two years to prepare and features works on loan from museums around the world, including two from New York\'s Metropolitan Museum of Art and seven from the Louvre in Paris. \"The Impressionists dedicated themselves exclusively to painting outdoors because they considered it fraudulent to paint outdoor scenes inside a studio. They thought that it made no sense to go outdoors to then paint a landscape from memory,\" said exhibition curator Juan Angel Lopez. Among the showpieces are Monet\'s 1882 painting \"Low Tide at Varengeville,\" depicting green seaweed in pools of water in front of drastic brown cliffs, and Van Gogh\'s \"Hospital at Saint-Remy,\" from 1889, portraying a man standing under a leafy tree in the foreground of a bright yellow house with green shutters. Paul Cezanne, Pierre-Auguste Renoir and Alfred Sisley are also represented at the exhibition that runs until May 12.