Amidol Types

Vlad Soare · Jul 23, 2010

Hi guys,

I notice there are two kinds of amidol. One is straight 2,4 diaminophenol (CAS 95-86-3). The other one is its dihydrochloride salt (CAS 137-09-7).
Do they both work the same in developers? Does it matter which one is used? Are there any practical differences between them, like, say, solubility, shelf life, etc.?

Thank you.

Gerald C Koch · Jul 23, 2010

With several developing agents like amidol. paraminophenol, and phenylenediamine the free base is not very stable and deteriorates quickly. Therefore the hydrochloride salt is often called for. Most devoping solutions contain an alkali so this is usually not a problem. But amidol is rather unique in that it is so active that it develops in acid solutions. I believe that most amidol formulas call for the free base. But it is important to use the form of the developing agent that the formula calls for.

In general the free bases are not soluble in water but may be soluble with the addition of other chemicals.

nworth · Jul 24, 2010

Gerald C Koch said:
With several developing agents like amidol. paraminophenol, and phenylenediamine the free base is not very stable and deteriorates quickly. Therefore the hydrochloride salt is often called for. Most devoping solutions contain an alkali so this is usually not a problem. But amidol is rather unique in that it is so active that it develops in acid solutions. I believe that most amidol formulas call for the free base. But it is important to use the form of the developing agent that the formula calls for.

In general the free bases are not soluble in water but may be soluble with the addition of other chemicals.

While Gerald Koch says is true, you can often make substitutions, especially when it is just where the crystal includes some molecules of solvent - different levels of hydration (or in this case hydrochlrorination). You do have to adjust the weight used to the equivalent weight of what is called for. In those cases where the solvent is a strong acid (usually hydrochloric or sulfuric), you may have to adjust the pH as well. In this case, you could substitute 1.67 grams of the hydrochloride for each gram of the free base. With amidol formulas, pH adjustment is usually not needed, but sodium carbonate or maybe even sodium citrate could be added to bring it up to spec. One quick and dirty method that is often used to adjust the pH of an acid material to near neutral is to dissolve it separately in a minimum amount of water and add sodium bicarbonate (baking soda) until the fizzing stops. This is not really an accurate or reliable way to do things, but it works most of the time, and a neutral solution made this way is usually close enough.

A more frequent problem occurs with sodium carbonate, which is commonly available in both anhydrous and monohydrated forms. Generally, formulas call for the monohydrated form, but some older ones call for the anhydrous variety. In this case you can use 1.17 grams of the monohydrate for each gram of the anhydrous form or 0.85 grams of the anhydrous material for each gram of the monohydrate.

Gerald C Koch · Jul 24, 2010

nworth said:
While Gerald Koch says is true, you can often make substitutions,

I think you misunderstood my post when I warned against making substitutions. Of course one can make sbustitutions in most of the chemicals in a developer. But I was speaking specifically about forms of a developing agent. For example, when substituting paraminophenol hydrochloride for paraminophenol one must account for the greater molecular weight and the added acidity. This requires a working knowledge of chemistry which some photographers may lack, hence my warning.

There is a problem with Amidol formulas since Amidol was a tradename and it is often unclear as to what form of the developing agent diaminophenol was intended. I don't think that the manufacturer ever revealed the actual form of the developing agent.

Vlad Soare · Jul 25, 2010

The amidol I have now is the dihydrochloride. But I have no idea which form the various formulae refer to. They all state simply "amidol". :confused:
Well, I guess I could mix two developers, one straight and one with 1.67 times more amidol, and then see which one works best...

c6h6o3 · Jul 25, 2010

2,4 diaminophenol dihydrochloride is what Artcraft Chemicals sells. To prepare a working solution add 30 grams Sodium Sulfite to 900 ml water, followed by 3 gm citric acid, 3 ml of 10% potassium bromide, and 8 grams of the amidol. Then add water to bring the volume up to 1 liter.

You don't need to mix them. What you have is what works in M.A. Smith's formula above. I've used it for years with outstanding results.

Vlad Soare · Jul 26, 2010

That's the formula I'm going to use, too. On Michael's site it only calls for 2ml of bromide, though he mentions in one of his articles that in 2005 he increased it to 3ml. I'm going to write to him directly and ask him about this.

c6h6o3 · Jul 26, 2010

VladSoare said:
That's the formula I'm going to use, too. On Michael's site it only calls for 2ml of bromide, though he mentions in one of his articles that in 2005 he increased it to 3ml. I'm going to write to him directly and ask him about this.

They've changed it to 3ml as their standard as Azo got colder. I find that 3ml yields a perfect print color on Lodima as well. I've used up to 5ml with good results.

jgjbowen · Jul 26, 2010

I've actually started a notebook of azo/lodima print colors. Developers used (so far) include Dektol, Neutol WA, MAS Amidol with 0,2,4,6,8,10 ml of 10% KBr/litre. These silver chloride papers are capable of delivering quite a range of tones with simple variations in the amount of KBr

c6h6o3 · Jul 26, 2010

Greg Davis said:
In graduate school we were given an assignment to choose three papers, four developers from The Darkroom Cookbook and six toners from the book, then make a print from the same negative using all the possible combination's.

72 prints from the same negative to complete the assignment? How long did it take you?

jgjbowen · Jul 26, 2010

Greg,

I'll bet what you learned about print colors from that exercise was priceless (at the time). I'll also bet the papers used likely don't exist anymore. I decided to do it with Azo/Lodima, because I THINK I have lifetime supplies with identical emulsion numbers in the freezer. Doing the exercise was well worth the effort, and thanks to the notebook I'll be able to find a combination that delivers the print color I desire without having to reinvent the wheel each time.

Shawn Dougherty · Jul 26, 2010

jgjbowen said:
These silver chloride papers are capable of delivering quite a range of tones with simple variations in the amount of KBr

Right on, I love it!

Vlad Soare · Jul 27, 2010

These silver chloride papers are capable of delivering quite a range of tones with simple variations in the amount of KBr

Click to expand...

Right on, I love it!

Indeed, that's what I like about it, too.
I used to love Forte Polywarmtone precisely for its ability to give different tones in different developers. I have no real experience with Lodima, having just started using it, but so far it seems to me that it's even more responsive to changes in development than Polywarmtone was.

Amidol Types

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