[pure-silver] Re: AW: Re: Any advice for purchase of densitometer.
- From: Sandy King <sanking@xxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Fri, 24 Dec 2004 09:05:04 -0500
There is of course no constant factor that one can add to the Blue
reading to approximate UV readings because the stain increases
proportionally to silver density. And the difference between the
Blue and UV reading is greater with Pyrocat-HD than with PMK. There
are densitometers that allow UV readings at about 370 nm and these
are quite popular with alternative printers using UV sensitive
processes.
The issue of printing VC papers with stained negatives is fairly
complicated. Years ago Phil Davis did some tests, using PMK, and
concluded that neither the Blue nor Visual reading is an accurate
indicator of effective printing density, and suggested that the best
reading would an intermediate one between Blue and Green/Visual. I
would suggest that this intermediate value is about half way between
Blue and Green/Visual for PMK negatives, and about two/thirds of the
way toward Green for Pyrocat-HD negatives. This is explained by the
fact that for a given visual reading there is more difference between
Visual and Blue readings with PMK negative than with Pyrocat-HD
negatives.
I address a number of issues related to stain in an article on pyro
developers that you can see at
http://unblinkingeye.com/Articles/PCat/pcat.html
Sandy
> > So IOW the density reading from a pyro negative may not be an=20
>> accurate=20
>> guide to the required contrast filtration if you're using VC=20
>> paper - which=20
>> is fair enough. As the instrument measures a wide colour=20
>> spectrum it will=20
>> presumably read both the silver and stain densities and give you an=20
>> effective total.
>
>I am doing some testing with Pyrocat HD (TMX and TMY), including
>measuring densities with a Macbeth TD 504. The problem of properly
>stained negs: the higher the silver density, the higher the stain
>effect. I tried using the "blue"-channel of my densitometer as an
>approximation to the UV-densities and compared the results with the
>silver densities measured via the visual channel. There is no constant
>factor like: "add 0,4 and its done".=20
>The Pyrocat stain has its highest effectiveness in the UV-Range which is
>AFAIK important for alternative processing. But for variable contrast
>printing I would guess the UV-part does not play such an important role.
>If I standardize my development for the G-bar-values obtained via the
>blue channel densities, I have to use grade 3,5 for printing. So in the
>future I will work with visual densities, this seems to correspond
>better with my printing technique.
>
>Michael
>
>
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