Serdar, both variants work. The green form has more Iron(III) compared to the brown form (roughly 19% against 14% - it's not exact science; use this as rule of thumb...), therefore you'll need more (~ 20-30%) of brown form. About the precipitate; just add the silver solution very slowly to the combined A (iron) + B (tartaric acid) solutions, almost drop by drop, while vigorously stirring the solution, also, try to double the amount of tartaric acid if you still have considerable amount of precipitate. (More acid will lead to a slightly higher contrast emulsion, which has less tendency to stain and fog - both qualities are desirable actually...) Let the solution stand a couple of days while occasionally shaking it, then let the solids settle in the bottom and filter it using a coffe filter. The solution will still work well. AND, definitely try gold-thiourea toning with Vandykes - you'll get a much much stronger image (w/o double coating) both in terms of darkness/dmax and longevity.