Gillies divided his energy between oil and watercolour; painting in oils was his studio routine, whilst he was happiest working in front of the landscape on his watercolour block. The originality and spontaneity of his landscapes on paper in pencil, pen and ink and pure watercolour, form the core of his reputation. When filmed in 1970, he spoke eloquently about his watercolour practice:
My landscape painting began with watercolour and a great part of my work has continued in this medium and I feel the peculiar qualities of the medium have had a strong influence on my conception of landscape… I have perhaps opened many people’s eyes to some unexpected, some subtle beauties in our daily surroundings. This has been, I hope, a by-product of my own enjoyment of what I perceive and my great delight in the very act of handling the paint.
Sir William Gillies is still highly underrated in Modern British terms. Born in Haddington, he trained and taught at Edinburgh College of Art, and did the latter as principal. He was a great influence on many of the next generation of the Edinburgh School. He himself studied in Paris with Andre Lhote and absorbed, variously, the work of Munch, Matisse, Braque and Bonnard. Still life and landscape oils tend to be composed studio pieces of subtle complexity. Watercolours are lyrically observed renderings of the Scottish Borders based on decisive pencil or pen drawings or for larger works, executed alla prima. Gillies had a long and fruitful relationship with The Scottish Gallery which continues in the secondary market.