The invention of the paint tube in England in 1841 enabled artists to transport their paint without it drying out. This made it easier to work outdoors, and plein-air painting became extremely popular. Artists like Gabriël, however, regarded the small, roughly painted studies they executed outdoors as belonging to a different category from their larger, more worked-up canvases. Large paintings, such as the Polder with Mills, were mostly made in the studio, on the basis of sketches and studies. One of the lesser-known masters of the Hague School, Gabriël paid close attention to his compositions, as can be seen in this sweeping polder landscape. An overcast sky, threatening rain, looms over a row of neatly ranked windmills. Though the colours are muted, Gabriël’s palette included a wide spectrum of greys and greens. In his eyes, every landscape was full of colour. ‘The more I observe, the more colourful and transparent the world of nature appears to be. And taking in the sky as well, it all looks totally different, but still in harmony. It’s wonderful when one learns to see—for that too has to be learnt. I shall say it again: our country is not grey, not even in grey weather.’