question about VDB

   I'm using the formula found in James (well, actually his formula divided
by 3). He calls for three 100 ml solutions--27 g FAC, 4.5 g tartaric acid,
12 g silver nitrate. I have, on four different occasions, mixed VDB
sensitize. In the first three I got a LOT of precipitate which I filtered
out. In all cases the remainder worked well and seemed consistent from
batch to batch. Since none of my sources mention a precipitate, much less a
very heavy one, I thought I was doing something wrong and made one change
each successive time. I switched to distilled water--no change. I added
the silver nitrate solution very slowly--no change except I realized the
precipitate occurred quickly toward the end of the addition. On batch
number four I attempted to stop at the first sign of precipitate and, sure
enough got only a little, though I had not added the full amount of silver
nitrate solution. This sensitize seems to act much like the first three.
    All of my chemicals are fresh and from well respected suppliers.
    So, do any of you get such a precipice and if so, what do you do besides
filter?
Charles Portland OR
Received on Sun Apr 9 15:20:32 2006