Van Gogh painted his self-portrait using the brightest green pigment available at the time. The strong and clear emerald- or Schweinfurtergreen. Beautiful, cheap and easily available, though very poisonous.
Van Gogh was probably aware of the risks involved, but being a painter devoted to colour, put matter over mind.
A strong, warm green like this, it seemed like dream never to be fulfilled. For thousands of years copper-greens were the main source for a more or less strong green pigment. Problem was the blueish hue that came with it. When in the 19th century the German Wilhelm Sattler started producing a new, bright green pigment, painters jumped to the opportunity.
Schweinfurtergreen, emerald green, became immensely popular, even though it soon turned out to be a killer in disguise. In fact, a pure arsenic.
To obtain a warm green, painters used to apply a warm yellow glaze over acopper-green or blue paint-layer. The result was often short-lived. The yellow glaze would vanish in time, but also the bright, cool copper-greens or blues could turn into dull browns. Many old landscapes and still-lifes are the victims of this unwanted change of colours.
An example of this deterioration is the landscape by Van Scorel. His once harmonious painting, depicting a lush garden in a fantasised landscape, has turned into a dark brown, lacking any connection with the severely faded background.
How different were the circumstances for Daubigny. He could chose from the newest pigments, strong, bright and durable. With Schweinfurter- and chrome-greens providing a pallet unknown before the 19th-century. Again chemistry supplied the means for a revolution in painting.