Sorry should read pryridinium (pyridine) dichromate, Kosar describes
pure form as consisting of water soluble orange red crystals. (The
impure form he says is brown or black with an unpleasant odour, not
completely soluble in water).
He reckons that it gives a twofold increase in printing speed compared
with ammonium dichromate. Naturally there will be an enhanced 'dark
reaction' so the sensitised coating may not be very stable.
I have a jar on the shelf which I've intend to dabble with shortly, I'll
let you know the result. I also want to look at the effect of
sensitising dyes in an attempt to increase the spectral response of gum
bichromate systems. Have you done any work on this? Of course the
presence of the pigment may mask the effect (if any)!
>
>There was a nice thread a year ago on pigments and particle sizes and how to
>measure them. Very illuminating.
I did suggest that the pigment should be dispersed in the gum by ball
milling, this should reduce the staining effect as well as producing a
uniform mix. I would interested to know your thoughts on this
Alex.
PS Who is this Mercke guy?
(Just Joking!!!)
-- Alex Nanson alec@norlex.demon.co.uk Gloucester. UK