RE: SG emulsion query

Ryuji,

Thanks, I suspected something of the sort. I have made simple chlorobromide
emulsions quite a few years ago, but now wish to make something *better*
than I did then. My working conditions are primitive but I already have a
reasonably good and fairly fast bromide formula, and wish to refine it by
increasing contrast and D-max. Maybe mixing with chloride emulsion is at
least worth trying... as I remember, CB emulsion is more prone to problems
with fog and black specks? Or would they behave as two separate emulsions
in one solution, i.e. the chloride component being so underexposed so that
it has little or no effect on the image characteristics?

I tried to find your silvergrain list a while back - is it deceased?

Thanks again,

Liam

-----Original Message-----
From: Ryuji Suzuki [mailto:rs@silvergrain.org]
Sent: 14 February 2005 19:23
To: alt-photo-process-l@sask.usask.ca; liam.lawless@blueyonder.co.uk
Subject: Re: SG emulsion query

From: Liam Lawless <liam.lawless@blueyonder.co.uk>
Subject: SG emulsion query
Date: Mon, 14 Feb 2005 18:56:39 +0000

> Will mixing a bromide and a chloride emulsion give the same or
> substantially similar result to making chlorobromide emulsion in the
> first place (from the same ingredients)?

No.

> If not, what diferences to expect?

Hard to generalize, but more later.

> In other words, if I
> can work out a chlorobromide formula by mixing two emulsions to get the
> desired image characteristics, will I still get the same thing if I then
> make it as a single emulsion?

Chlorobromide emulsion is not made by mixing AgCl and AgBr
emulsions. Instead, each single crystal is a mixture of AgCl and AgBr.
If two separate emulsions are mixed, they must be mixed in a certain
way so that one dissolves and grow on the other. The characteristics
of AgClBr emulsion varies depending on the profile, Cl:Br and
distribution, in addition to crystal size, sensitization technique,
and other factors. For example, some emulsion may have more Br in the
core, and others in the shell, the rest may be homogeneous mix
throughout. These factors together make a large difference.

If you are starting out in this area, I generally recommend to begin
with bromide printing emulsion. It is a lot less frustration to work
with than chlorobromide or chloride, though making chloride or
chlorobromide emulsion is easier.

--
Ryuji Suzuki
"Well, believing is all right, just don't let the wrong people know
what it's all about." (Bob Dylan, Need a Woman, 1982)