Umber is essentially clay, and this variation on the PBr7 pigment is the lighter (un-burnt) version of this classic earth tone that originated in the Umbria region of Italy.
Historical azurite, from copper carbonate minerals, lacks the stability and durability required for modern painting, this mixture affordably approximates azurite's deep greenish blue.
Part of the earth tone family, Yellow Oxide's is slightly more opaque than it's neighbours (Yellow Ochre) and less red, but with similar lightfastness and durability.
