>The same phenomenon can occur with the right emulsion *in* a layer of
>gelatin. P.O.P. (Printing Out) paper was/has been available in both
>collodion emulsion (ca. 1885-1920) and gelatin emulsion (ca. 1885 - right
>up to today with Chicago Albumen Works papers)
But the general point remains that negs for normal develop out, and thus greatly
faster, silver gelatine emulsions are too thin for printing out processes even
for cyanotype where for a print with good gradation and a full range of tones
one needs a negative a full stop more dense than is needed for a silver gelatine
print. Of course one can 'get away' with less.
Judy said:
>Self-masking occurs in a printing-out process. As the shadows darken they cut
down on the light getting through to the emulsion. >Whether the light sensitive
materials are on the paper or in a layer of gelatine is ancillary or immaterial.
We were talking about negs designed for silver gelatine being used for printing
out onto a platinum palladium emulsion. In VDB, Brown, kallitype,cyanotype,
platinum and salt the phenomenon occurs as I described.
As Judy and Luis point out there are other printing out processes such as POP,
and albumen, where self masking also occcurs.
On reflection modern silver gelatine papers can be made to print out. But it is
such a long time since I did so that I cannot remember if I used a punchier
negative.
Terry King