This color contains the following pigments:
Fe7(CN)18(H2O)x or C6FeN6H4N
Prussian Blue is a semi-transparent, deep cyan-blue with a greenish undertone and a very high tinting strength unequaled by most pigments. It is similar to Phthalo Blue unless mixed with white, when it gives up intensity and becomes smoky. It can behave erratically and less reliably in oil and watercolor form depending on its manufacture. For permanent painting Phthalo Blue is considered a more reliable choice.
Prussian Blue is lightfast and permanent in all techniques except for fresco. When mixed with Zinc White in watercolor or tempera form, it fades upon exposure to light and completely regains its chromatic strength in the dark. Modern manufacturing techniques have made this tendency less of an issue in recent years
Prussian Blue is moderately toxic if ingested. It will emit toxic hydrogen cyanide gas if heated, exposed to ultraviolet radiation, or treated with acid.
"The first of the modern pigments," Prussian Blue is the first artificial pigment with a known history. It was discovered by accident in 1704 by the Berlin color maker Heinrich Diesbach, who was trying to create a pigment with a red hue by mixing iron sulfate and potash. The potash Diesbach purchased from a local laboratory had been contaminated by animal oil and blood during previous experimentation. The resulting mixture yielded a very pale red that changed to purple and then deep blue when he tried to concentrate it. Since previous blue pigments came from lapis lazuli, an expensive stone, Diesbach’s discovery was extremely important for artists of the time.
Burnt Sienna is a warm, mid-brown color formed by burning the yellow-brown limonite clay called Raw Sienna. It ranges from semi-opaque to semi-transparent due to the combination of its opaque, red-brown mass tone and its transparent, orangey undertone. It is an excellent mixing complement for blues and greens and creates salmon or peach colored tints when mixed with white. It can be useful for subduing bright colors and does not get chalky in dark mixtures.
Burnt Sienna has good permanence and is considered one of the most versatile of the permanent pigments.
Burnt Sienna has no significant hazards.
Burnt Sienna has been used as a pigment since prehistoric times, but its current name came about during the Renaissance. It comes from the city of Siena, in Italy, and is short for terra di Siena, meaning earth of Siena. Sienna was famous for the mining and production of earth pigments from the Renaissance until World War II. Due to the depletion of clay deposits in Tuscany, Italian siennas now come from other areas, including Sicily and Sardinia.