Chemistry question Potassium Bromide?

**Shen45** · 6-Dec-2006, 19:21

I have a developer formula for paper but don't have the Potassium Bromide.

If I leave the Pot Bromide out what if any effect will that have on the tone of the paper when developed ?

The formula is for D72.

Steve Nicholls

**Glenn Thoreson** · 6-Dec-2006, 19:59

D-72 is Dektol, for all practical purposes. The bromide is the restrainer. Leaving it out would, I think, make the developer more active. Dektol is pretty active the way it is. I don't know if leaving it out would harm anything. It would give a colder tone to a print, I think. I add bromide to Dektol to add a bit more warmth to Ilford MG Warm Tone FB.

**Shen45** · 6-Dec-2006, 20:27

Originally Posted by Glenn Thoreson

D-72 is Dektol, for all practical purposes. The bromide is the restrainer. Leaving it out would, I think, make the developer more active. Dektol is pretty active the way it is. I don't know if leaving it out would harm anything. It would give a colder tone to a print, I think. I add bromide to Dektol to add a bit more warmth to Ilford MG Warm Tone FB.

Thanks Glenn,

I presumed the Bromide helped give either warmer or cooler depending on amount. I will try it without and see what the result is.

**Jason Greenberg Motamedi** · 6-Dec-2006, 22:29

For what it is worth, KBr is really cheap. I paid about $15 for 5kg a few years ago.

**paulr** · 6-Dec-2006, 22:42

The main purpose of the restrainer is to reduce fog. So you'd expect to see more fog in your negatives than without it, especially if you're using high concentrations or long developing times. It might also slightly effect the tonal scale, but I'm not sure how. I've been happily using a film developer for years that has no restrainer in it, so it isn't always important.

a bit of fog isn't a big deal with film, since you can print right through. the KBr is much more important in paper developers, since you don't typically want fog muddying up your highlights. KBr also effects image tone, adding warmth in some cases (but intensifying the green tint in many other cases). Old timers often kept a solution of it on hand to add to the developer for subtle color control, but I don't think too many contemporary papers take well to this.

Benzotriazole can be substituted in any formula. Technically it's an anti-fog agent, not a restrainer, which means it works in subtly different ways. It tends to push print color towards blue. I haven't experimented with it, but I assume you could substitute it for KBr in any film developer without major consequences.

**John Cahill** · 7-Dec-2006, 07:52

Steve,
I think there should be some kind of restrainer used in D-72 but if you try it without, let us know the results. My understanding, though, is that after a few prints, the D-72 will have bromide released into the solution by the developing process.

Since I like cold tones, I use benzotriazole in a modified Ansco 103 paper developer. If you intend to replace Potassium Bromide by Benzotriazole in D-72, you should still include some Potassium Bromide in the formula to keep your print color constant. There needs to be some bromide added, apparently, for paper development.

**John Quinn** · 14-Dec-2006, 02:37

Steve,
Potassium Bromide
Try Ace Chemicals, Mooringie Ave.,Camden Park - if they can't help give me a ring,( Quinn J.A. in Business section of phone Book) and I may be able to locate some for you.
John Quinn