>I have started working with the Van Dyke and cyanotype processes with
>varying degrees of success. One of the things that I haven't seen much
>discussion on (though I certainly may have missed it) is how best to
>spread the sensitizer to ensure an even coat. I currently am using a
>foam brush and generally try to make even strokes in al four directions.
> It seems to work okay, but I'm wondering if it's the best way to do
>this.
My own teaching and personal experience an our business help line
suggests strongly that a glass coating rod is the best way to coat. The
coating rod is bacically some form of T-handle attaced to a 3/8 inch glass
rod cut to the smaller width of the paper to be coated, that is if you want
to coat a 16x20 print, the rod should be 16 inches long. The use of a
smaller rod will lead to the edges leaving marks in the print.
I have also been doing some intensive investigations into the pt/pd process
and have one tip that might seem heretical to many and that is the use of
Kodak Photoflo in the emuslion. The use of 1 drop of straight KPF to @ 20
total drops of emulsion will greatly enhance the dMax and prevent much
washoff. It appears that we have over the years become obsessive with a good
hard sizing. The KPF's role is to cut through the sizing letting the
emulsion penetrate into the paper. I am also using 1 or 2 drops of glycerine
per 20 drops total emulsion as this seems to moderate the "sink" effect and
give more time to coat, it also slows the drying somewhat as the humidity
here in Santa Fe at often is less than 20%. Mike Ware suggests the use of
Tween in his Argotype process notes to do something similar.
One caveat however, I've only been doing it with 4x5 and 5x7 prints
and all coated with a rod. I feel that a 16x20 print could only be coated
with a rod since the "sink" rate of the emulsion is rather fast and the use
of a brush would only lead to streaking. I have also only had goood results
with moderately sized papers such as Cranes Platinotype and Cranes Parchmont
wove, unfortunately I get tremendous grain with Martin Axon's Platine paper.
Dick Sullivan
Bostick & Sullivan
Santa Fe, New mexico