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1/3 on Degas and his methods.
Degas -- Captured in Silver
Artists of today have very different views on if and how to use modern technical innovations in art. The span ranges from the representative purists who always paint from life, be it indoors or outdoors, to the digital computer artist who never touches paper or canvas.
Painting from reference photographs definitely falls into this category. It is often claimed that the old masters always painted from life, or used sketches from life, or even were so well educated they could invent immensely complex scenes and make them look real.
In pastels, Edgar Degas is one of the most revered masters of old. Art-books are filled with admiration for his spontaneous style and ability to sketch quickly on location, catching ballerinas in action. He would never have resorted to copying a photograph, it is claimed.
It is not widely known (not among artists) that Degas was an enthusiastic – overenthusiastic, his friends thought – photographer, owning a camera that captured the image to silvered glass plates reminiscent of the earlier Daguerreotype (an early form of photography). Although the paper film roll had been recently invented, a reason for using glass plates could have been that they gave sharp images, but could also be manipulated in several ways, and it is known Degas indeed did manipulate his plates with chemicals.
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See the whole article, with pictures, by clicking on this link to the pdf on Pastel Guild of Europe's site. Page 2.