Natural Cassel Earth is also sometimes called Van Dyke Brown, Bituminous Earth, or Cologne Brown. We have heard it described as occurring in or near bogs and/or peat deposits, but sometimes it is a kind of earth. At the time of this writing, there does not seem to be any availability of natural Cassel Earth. Some of the last companies we knew of who made NBr8 into paint ceased to sell it around 2020.
The lightfastness of this pigment varies tremendously depending on the pigment source. Even some of the better lightfastness ratings for NBr8 show some lightfastness loss in tints. Though it is no longer available, Williamsburg listed their particular version as ASTM II equivalency.
We have used that particular variety, and found their description to be apt: "When it is milled in oil, it maintains a coarse feel and when painted from the tube in full masstone, catches light on a textured surface to produce a dark, rich, dusty brown. It has a warm, semi-transparent, brown undertone that when drawn thin, shows the coarseness of the pigment. It also has extremely weak tinting strength and although brown in every other way, tints with white to a fairly neutral grey." Today, Van Dyke Brown is usually a blend of pigments (convenience blend) to create a deep brown-black.
