Mixing Vandyke Sensitizer

[thefizz]

Is it normal for Vandyke sensitizer to look very cloudy when mixed fresh from the raw chemicals?

 

[Herzeleid]

It can happen sometimes, I think it depends on the chemicals, temperature etc. If you are having too much precipitate after the solution settles, increasing tartaric acid gradually to 4gr helps a lot.

 

[thefizz]

Thanks, I’ll add more tartaric acid next time. I heated the bottle of sensitizer and that helped a little and then I filtered it, so much better now.

 

[koraks]

When I do Van Dyke, I always prepare the solution fresh from concentrates of the three constituents. This way I have fresh sensitizer at any time, which is nice as I found that a mixed batch would eventually silver out and produce poorer results than fresh. When I mix the FAC and silver nitrate, the solution always clouds. I add drops of tartaric acid solution until the stuff clears. It's immediately ready for use (contrary what is stated in guides that the solution needs to age).

The amount of tartaric acid, besides clearing the sensitizer, has additional effects:
* Less tartaric acid results in lower contrast and a smoother appearance of the image, but dmax suffers below a certain point.
* More tartaric acid results in higher contrast and a more grainy appearance of the image, with high dmax, but shadows tend to fill in beyond a certain point.
The sensitizer solution needs to be perfectly clear in order to coat well, so that poses a hard lower limit to the tartaric acid concentration.

Within a narrow bandwidth, it is therefore possible to accommodate differences in negative contrast using the tartaric acid concentration, although the effect is much less pronounced than when dichromate is used. However, due to the reduced dmax when lower concentrations of tartaric acid are used, I personally find 4% the best overall compromise between smoothness and dmax.