Viridian Green (also known as Guignet's Green) is an inorganic pigment made from hydrated chromium oxide. The process by which it was created was initially kept secret, but it was eventually patented in 1859. Viridian quickly became popular due to its deep color, stability, permanence, and non-toxicity. Viridian Green is a very deep, cool, blue green that can be too intense for many artists. However, it is a very popular color for mixing. Mixing Viridian with earth tones like yellow ochre can create unique, subtle, warm organic greens. Viridian can also be mixed with Alizarin for dark grey hues, and violets for shades of blue-black. The lack of yellow in Viridian makes it ideal for mixing muted gray greens, which are especially appropriate when painting the American Southwest.