Kremer Pigmente GmbH & Co. KG     Kremer Pigments Inc., USA  

Ploss blue is neutral verdigris, also known as "crystallized", "distilled", or "purified" verdigris, is neutral copper acetate Cu(CH₃COO)₂.H₂O. The acidic solution of copper can be neutralized with lime, resulting in blue-green crystals of especially brilliant luminosity. The crystals dissolve entirely in water without decomposition. Basic verdigris (see also 44450) is formed when acetic acid vapor, water vapor and air act on copper. The copper becomes covered with a bluish green crust, which is then scraped off. Around the twelfth century, the verdigris production centered around the area of Montpellier, in the South of France, were the wine industry was flourishing.

This pigment is much more vivid than in colour than azurite, almost comparable to our fluorescent blue. Although it is not stable in acidic media such as linseed oil, it is suited for fresco, egg tempera and watercolour.

The colour change is less pronounced with neutral verdigris in oil and egg tempera than it is with basic verdigris. Ploss blue reacts with binding media; with resins it forms copper resinates; with oil it forms copper oleates; and with proteins, it forms copper-protein compounds. Neutral verdigris is known to promote the drying of oil-media, a property which was mentioned in the literature.

H. Ploss describes the production of this colour in his book, "A Book about Old colours", with a reference to a colour book dating back to 1500 from Trier (Germany). The name of this colour was chosen in his honor.