An intense deep greenish blue that was from its invention in 1704 to the mid 20th century the most important deep blue available to artists. Problem was there is a great deal of variety of quality between manufacturers of the color so it was variable in permanence, the best being excellent, but some might turn brown or fade. However artists accepted these limitations because the color is so useful. When Pthalocyanine Blue was discovered in the 20th century it quickly replaced the genuine Prussian Blue because it was generally better.