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Abdi,
Before using the Van Dyck brown, check the pigments listed on the side of the tube. If it is true Van Dyck brown (Pigment listed as NBr 8), don't use it. It is known to be very weak and fleeting. Not every tube of van Dyck brown is made of this pigment, though. Most manufacturers mix some pigments to get the "look" of the v.D. brown using carbon or lamp black (PBk 7 or PBk 6) and some combination of Burnt Umber/Sienna (PBr 7). Also, some manufacturers' vD brown contains yellow ochre. The bottom line is, if the pigment list on the tube indicates it has NBr 8 in it; don't use it.
Asphaltum is another of those pigments, like van Dyck brown, that quickly went out of use when its negative qualities were discovered by the late 19th century, and better pigments were substituted for it. Gamblin has recreated the "look" of asphaltum, but with permanent, reliable pigments. You can make your own Asphaltum or vanDyck Brown with black, burnt umber/sienna, and yellow ochre or cad yellow medium (very little of the latter or it becomes too greenish). For the blacks in these mixtures, I would recommend using only lamp or carbon as they are the best and most thorough driers. However, the very addition of the umber aids in the drying process.
Hope this helps.
Juan
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