Chemically this material does not differ from the natural product, both being barium sulphate BaS04 but blanc fixe, as the material is best known to the trade, is amorphous in texture, while the natural product is crystalline. Under the microscope this is best discovered, because no matter how well ground and how finely floated the natural product may be, it will reveal its crystalline form under this test. The practical consumer, however, need not go to that trouble, as he can readily tell from the bulk or specific gravity of the two pigments which is the natural and which the artificial. Blanc fixe in comparison with ordinary barytes is more opaque, much finer to the touch and absorbs twice, even three times, the amount of color; hence it is a far better extender for white pigments than the natural barytes. The reason that it is not in more general use for this purpose is its higher cost, which is over twice that of the very finest floated natural product and its greater absorption of oil. A good grade of blanc fixe in powder will weigh from 10 to 12 pounds per gallon, and while natural barytes requires on an average of 8 pounds of oil to 92 pounds pigment for a medium stout paste, blanc fixe requires not less than 15 pounds of oil to 85 pounds of the dry powder, and when extra fine even as much as 18 pounds of oil to 82 pounds of pigment.
The greater oil absorption is not due to its lower specific gravity (average 4.16), but entirely to its fine division. Blanc fixe is produced by adding sulphuric acid to a solution of barium chloride when barium sulphate is precipitated as a fine white powder. The precipitate is well washed with warm water to remove all traces of acid, then if wanted in the dry form it is filtered, pressed, dried at low heat and pulverized. The bulk of the product, however, is after washing permitted to settle, the water drawn off, the pulpy mass thrown on filters until it consists of about 70 per cent pigment and 30 per cent water and sold in that form to the trade.