How to eliminate the precipitate from Van Dyke Brown solutions
Categories: Van Dyke Brown — Tags: Acido tartarico, Granulosità, Precipitato
Translations:
italiano •
Lots of Van Dyke Brown printers lament that a precipitate form inside a Van Dyke Brown solution, obtained during the preparation of the solution itself, or more precisely just before finishing to add C inside A+B, following the conventions and quantities of the VDB classic formula like the Wynn Whyte style says.
Not everyone obtains this precipitate and the principal reason is that ammonium ferric citrate is not a well-defined chemistry substance. (go to Mike Ware page for same examples), that means it changes from distributor to distributor and often from bottle to bottle.
VDB precipitate description
The precipitate I obtained, which has an aspect similar to the one described by many other printers, has a light grey-green color, a milky aspect, as it would be a suspension of fine grey powder. Just to let you understand, it has a color similar to mustard mixed with oil. Once obtained a homogeneous cream, in a ten-minute the oil starts separating from mustard and the visual aspect is, apart from the color, similar to the one obtained with VDB solution.
The precipitate is obtained when 2/3 of C solution has been added to A+B. Suddenly a precipitate takes form, in big quantities, as solution would have reached a saturation point and adding an only drop of C would bring immediately to the precipitate we were talking about. No matter if you mix more slowly, no matter if you let the agitator on for hours: the precipitate is formed and you can’t dissolve it anymore.
If you let the bottle aside, the precipitate settles on the bottom, occupying a volume that is almost the half of the entire solution. Agitating the bottle gives an opaque solution that produces an irregular, granular, maculated and black streaked print. Using the solution on the top of the precipitate, the print is correct, but the volume of solution we could use would only be the 50%. Analogously, filtering the solution means losing a big volume of salts, potentially composed of silver that, if inside solution, could be used to form the image. As the silver nitrate is expensive, it would be better to avoid this settle.
Other settlements in Van Dyke Brown solutions
This precipitate has not to be confused with other settlements obtained in Van Dyke Brown Solutions. It has nothing in common with “silver plating”, which is a fine film of metallic aspect, such a thin mirror. This film settles on the inner surface of the bottle or of the emulsion surface if it’s let at rest for some weeks. It has also nothing in common with the fine precipitate that settles on the bottom of bottles after some days, generally a poor quantity of fine dark green powder. These two types of precipitate usually interest a little percentage of the solution and do not cause problems during the print.
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