Aureolin is a pigment used in oil and watercolor painting. Its color index name is PY40 (40th entry on list of yellow pigments). It was first made in 1848 by N. W. Fischer in Breslau and its chemical composition is potassium cobaltinitrite

Potassium cobaltinitrite

Potassium cobaltinitrite, IUPAC name potassium hexanitritocobaltate, is a coordination compound with the formula K3[Co6]. The anion of this yellow-coloured salt consists of a cobalt center bound to six nitrito ligands. It is insoluble in water and is precipitated as yellow solids.It was first made...

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Aureolin is rated as permanent in oils but darkens and fades easily in watercolors. It is a transparent, lightly staining, light valued, intense medium yellow pigment. It is a rather expensive pigment and sold by several manufacturers of oil paints such as Grumbacher

Grumbacher

Grumbacher is an American manufacturer of art materials. The company offers products for artists including oil, water-miscible oil, watercolor and acrylic paints, as well as brushes and painting media. It was founded in 1905 by Max Grumbacher and was a subsidiary of the Sanford L.P., a Newell...

, Michael Harding, and Holbein. However, the pigment was never popular as an oil color and is much more widely available as a watercolor from manufacturers such as: Winsor & Newton

Winsor & Newton

Winsor & Newton manufactures a wide variety of fine art products including: oils, alkyds, watercolours, acrylics, pastels, brushes, canvases, papers, portfolios, and distributes the Derwent pencil sets.-History:...

, Talens Rembrandt, Rowney Artists, Sennelier

Sennelier

Sennelier is a French brand of art supplies famous for their hand selected pigments. They produce oil paints, water colors, gouache, pastels, india ink and many other mediums....

, Art Spectrum and Daniel Smith.