[alt-photo] Re: Gelatin

[Ryuji Suzuki]

The phrases "physical ripening" and "chemical ripening" refer to steps used in 
producing silver-gelatin emulsions, and the major difference is in trace amounts 
of impurities. In fact, what you described suggest that those gelatin products 
were designed for pre-WW2 era, since modern emulsions are made with very much 
purer gelatin with a controlled amount of chemical agents intentionally added, 
rather than relying on incidental components of gelatin.

What this means is that these distinctions are unimportant for most other 
purposes. You might want to test the available samples for viscosity, how 
gelatin stiffens when chilled, and other rheological and optical properties 
rather than trace amount of chemical impurities.

--
Ryuji Suzuki
"If the President will let them off the hook and let them become kinder, gentler
and flabbier, we'll all be grateful."
(James Pinkerton, then a White House staff, 1990)


Jacques Kevers wrote:
> Hi,
> I'm considering the purchase of gelatin - photographic grade (250+ bloom)
> used for oil printing mainly.
> I got a quote for 2 quite similar types: physical and chemical ripening.
> The physical has a slightly higher bloom grade, the chemical ripening type
> contains significantly more calcium (4500mg/kg instead of 100).
> Any idea about the importance this could have when used with other
> processes?
> Thanks in advance, and best regards from Belgium
> Jacques - waiting for Christina's book :-)
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