Also known as Thénard's blue or Dresden blue. Discovered by Thénard in 1802 and manufactured a short time thereafter. It is a compound of cobalt oxide, aluminum oxide and phosphoric acid. Cobalt blue is very bright and may have a greenish undertone, unlike ultramarine blue. It was widely adopted, along with synthetic ultramarine, by nineteenth century painters such as Renoir, Monet, Morisot and Sisely. Because of its relatively high cost, nineteenth century painters would commonly mix it with synthetic ultramarine blue. It is very stable and can be used for all painting techniques.