From: Judy Seigel (jseigel@panix.com)
Date: 01/20/03-01:59:31 PM Z
On Mon, 20 Jan 2003, Neil Miller wrote:
> One thing that continues to plague me is mixing the solutions without
> forming a precipitate. I had three attempts over the weekend. All
> three had this in common - each part (a, b and c) mixed with distilled
> water. 'A' added to 'B' and mixed thoroughly. 'C' added to this
> mixture drop-by-drop. The first attempt was at room temp, not very warm
> at this time of year. As in the other two attempts, I dropped the 'C'
> solution through a syringe drop by painful drop. A bright green milky
> solution formed, the precipitate gradually settling a little. 2nd
> attempt - all solutions heated to 30 degrees centigrade - still a
> precipitate formed, but much less this time. 3rd attempt - all
> solutions at 55 degrees, mixing vessel kept in water bath to maintain
> temp. No precipitate at all, but next morning a very slight precipitate
> had settled at the bottom of the brown glass bottle. This is the
> solution I have used to coat the next batch of test paper. Do you think
> that the other solutions will be OK if I filter them?
Neil, I've never seen a precipitate when mixing the AB& C for VDB... it's
not normal to the process. The one time we saw anything at all suspicious
it turned out that the "distilled" water was a fake... just tap water
according to the chem lab, & it got cloudy right off when we mixed in the
silver nitrate.
Since you're apparently not getting it until you add the silver to the
other two, it's probably not the water. My hunch would be the FAC. have
you made cyanotype with it? That's only a one-way proof -- if you get a
blue precipitate when you combine the A & B with cyano, your FAC is bad.
If not of course it could still be bad I guess... but anyway, that's where
I'd look first.
When all chems are right, you can add the silver at a fairly rapid pace,
stirring... even if a bit of white forms at the point of the pour, it very
quickly goes back into solution.
However, I'm assuming your B is tartaric -- maybe it's not...(it should
be, because the other acids make an inferior emulsion IME & that of others
I trust) --- how much are you using?
A bit of precipitate at the bottom of the bottle is no big deal. You're
decanting from the top anyway, if it mattered, which it doesn't. VDB isn't
rocket science, you've just hit a few bumps. I think any VDB solution gets
a precipitate after a while... and if it comes out on the paper, IME, it
dissolves right back as you coat.
Judy
This archive was generated by hypermail 2.1.5 : 02/21/03-10:44:17 AM Z CST