RE: palladium drydown and developer

Hi Clay,

My take / understanding is: when you coat the paper with some kind of
reflective medium (gelatine, gum, wax and polyurethane wood finish as I do),
the reason of the darkening and contrast increse in the shadows is caused by
the fact that the higher refractive index of the coat causes some of the
refracting light stay in the layer... Think of the mirror effect water
causes when the light hits it surface from beneath with angles lower than xx
(was it 38? - don't remember exactly - whatever you understand what I mean).
Since less light is reflected back (and kept in the coating), density
increases.

Maybe your theory with fibers is also effective in this phenomenon but I
think the actual/main reason/cause of the dmax increase is what I describe
above.

Regards,
Loris.

-----Original Message-----
From: Clay [mailto:wcharmon@wt.net]
Sent: 21 Temmuz 2006 Cuma 13:51
To: alt-photo-process-l@usask.ca
Subject: Re: palladium drydown and developer

...

The other phenomenon that has not been mentioned is the microscopic
'fuzzing' of the paper surface that occurs as paper dries. This seems to
affect the dark shadow areas much more. It is really more accurately called
'dry-up'. If you slap a wet pt/pd print on a reflection densitometer, you
will get a much higher reading (in the
1.8 range) than you will a few hours later after it has dried. The tiny
fibers of the paper then stand proud and cause a loss of reflection density
that in the best of cases will give you reflection densities in the
neighborhood of 1.4-1.5. This is almost a full stop of reflection density
loss.

As to what can be done to mitigate this effect, I have found that very light
gelatin sizing (in the 1% range) can help to a degree.
Another approach is to deal with this after the print is dry and apply
either wax or subsequent gum coats. I have a waxed vellum print that has
measured Dmax of 1.9 using several layers of Gamblin cold wax medium.

My personal preference is for additional layers of expose gum, since it
offers so many options for color manipulation of the image.
Finally, a coat of Liquitex Gloss medium diluted 1:8 will also have the
effect of causing a measurable (though relatively minor half
stop) increase in Dmax. Again, I think this is because it causes the
microscopic fibers to lay down and behave.

...
Received on 07/21/06-05:48:48 AM Z