Re: physical developers

"Again, from what Dr. Henry found physical development has no advantages in
practice. Although it is claimed ot produce extremely fine grain Henry found
that it was no finer, and sometimes coarser, than D-76.
It would probably be intresting to experiment with."

For Lippmann emulsions physical developers may have some advantages though.
They are able to produce grain sizes smaller than 10nm...

Martin

----- Original Message -----
From: "Richard Knoppow" <dickburk@ix.netcom.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Tuesday, August 24, 2004 7:51 AM
Subject: Re: physical developers

>
>
> -----Original Message-----
> From: Bill William <iodideshi@yahoo.co.jp>
> Sent: Aug 23, 2004 9:29 PM
> To: alt-photo-process-l@sask.usask.ca
> Subject: physical developers
>
> Speaking of physical developers, anyone here use them?
>
> Got any formulas / experience you would like to share?
>
> Ray
>
> __________________________________________________
> I have no direct experience but will refer you to Richard Henry's famous
book _Controls in Black and White Photography, second edition. This has
gotten quite rare but some libraries may have it. In it Dr. Henry reports on
some controlled tests using the O'dell formulas. His conclusions are that
the claims made for it are not borne out in practice. Haist has a short
section on physical developers in _Modern Photographic Processing_. For
those not familiar with the term a physical developer is one that plates
silver onto the development centers of the exposed halide particals rather
than converting the halide to silver, a process known as chemical
development. It is likely that some fine grain chemical developers have some
contribution from solution physical development.
> If a plain fixing bath is used it is actually possible to develop the
latent image in fixed out film by means of a physical developer. This is
mostly of academic interest but it is a demonstration of how the development
specks produced by light remain in the gelatin even when the silver halide
is removed. The sensitivity of the film is very much reduced, perhaps on the
order of ten or twenty times when this process is used. I am away from my
references now so am going on memory but I think this is correct at least as
to order of magnitude.
> Again, from what Dr. Henry found physical development has no
advantages in practice. Although it is claimed ot produce extremely fine
grain Henry found that it was no finer, and sometimes coarser, than D-76.
> It would probably be intresting to experiment with.
>
>
>
>
>
> Richard Knoppow
> dickburk@ix.netcom.com
> Los Angeles, CA, USA
Received on Tue Aug 24 00:32:25 2004