Chloride/Bromide ratio in ClBr emulsion

[di de]

Hello,

From what I've read (not much), Chloride and Bromide are generally in equal parts (in weight) in ClBr emulsion.
What effects are we supposed to get if we modify this ratio ? say 1:2 or 2:1

 

[dwross]

Both chlorobromide and bromochloride papers used to be made by most companies. The designations depended on which halide had the greater presence. Whichever direction you go, you get more of the defining characteristics of completely chloride or bromide emulsions, including emulsion color and how susceptible to color change from toning. Don't change the amounts by scale weight, however. Use "reacting proportions." see p.65 of T.Thorne Baker's book, Photographic Emulsion Technique for a table of reactants.
http://www.thelightfarm.com/BookImages/Baker.pdf

 

[di de]

Thank you

Chloride tends to be warmer, right ?

 

[Photo Engineer]

I have seen just about every possible ratio of these two halides in emulsions. Warm tones were generally obtained by using other chemicals in the emulsion or changing the order of addition. For example, Copper salts were used to make warmer toned emulsions.

PE

 

[di de]

ok, thank you
copper chloride will be part of my next purchase

 

[thio]

Increasion of Cl:Br ratio will tend to increase contrast and warm tone but decrease speed.

 

[thio]

A lot of paper emulsion formulas by Steigmann, contact-speed and enlargement-speed, various contrast and tone (cold and warm). Please note (and calculate) the various Cl:Br ratio.

A. Steigmann - 'Les sel de cadmium dans les emulsions riches en chlorure d'argent' // IX Congr. Intern. Phot. (1935)

PS. Unfortunately I can not attach the pdf (1.4 Mb) but I can send it by email or fb.

 

[dwross]

I have seen just about every possible ratio of these two halides in emulsions. Warm tones were generally obtained by using other chemicals in the emulsion or changing the order of addition. For example, Copper salts were used to make warmer toned emulsions.

PE

Also, a ClBr emulsion that is more or less balanced for the two halides is very flexible as far as development color goes. A print can be made in any tone from black to brown. The easiest way to do this is to add KBr to the developer and considerably increase the exposure time. Attached is an image of three prints stacked during scanning. All the same ClBr emulsion, same basic developer, just with varying amounts of added 10% KBr solution and increased exposure time.

 

[thio]

I agree with Denise

 

[di de]

thanks

thio, I don't know if my email is visible but I'm interested in the article you mention

 

[di de]

Also, a ClBr emulsion that is more or less balanced for the two halides is very flexible as far as development color goes. A print can be made in any tone from black to brown. The easiest way to do this is to add KBr to the developer and considerably increase the exposure time.

I was wondering if the same result could be achieved by a greater excess of bromide in the emulsion ?
And on one hand, bromide in the developer gives warmer tones, but on the other hand, pure bromide emulsions aren't warm toned... is it the presence of chloride that permits a combined action with bromide to yield warm tones ?

 

[Photo Engineer]

If that were so, then the many emulsion makers would not have resorted to all of those exotic chemicals to get the tones as well as a good curve shape.

PE

 

[di de]

It makes sense...