Hello, everybody

I finally had a chance to buy Pyrogallol and am going to test it soon. It would be helpful if you answer a couple of my questions:

As far as I know, to be able to act as a developing agent the Pyrogallol needs an alkaline environment (pH > 7, even pH > 9), and in spite of staining it has a "tanning" effect in highlights.

My first question is almost terminological: Is the "tanning" the same thing as "hardening"? Does it means the physical properties of gelatin get changed? Does a sort of texture appear on the negative?

Q2: does the tanning (hardening?) take place in neutral or slightly acid environment (pH <= 7)?

Thank you

-- Andrey Vorobyov (AndreyVorobyov@hotbox.ru), April 26, 2002

Answers

Andrey,

Pyro developers need alkaline conditions for tanning and stain development. The sodium metaborate in the PMK formula, and sodium carbonate in other pyro formulas provide the pH needed. Offhand I don’t remember the exact pH required, but it is strongly alkaline. See the "Book of Pyro" for details.

Tanning does harden the gelatin and you very clearly see a texture on the negative when it is still wet. The raised relief image is less apparent when the negative dries. It is recommended to use a non- hardening fixer because hardener is said to interfere with the desirable stain formation. Acid stop bath is to be avoided also. I sometimes use Kodak Rapid fix (without adding the hardener) and despite the fact that this fixer is formulated slightly acidic, I still get good stain. In fact, I avoid the alkaline after bath, which gives me too much stain. I print Pd/Pt and very heavily stained negatives have outrageously long print times. For silver printing this may not be a problem because stain is what gives pyro negs their magical properties.

If you want all the details you really should get Gordon Hutchings excellent “Book of Pyro”. Also consider trying Pyrocat-HD, a catechol based staining/tanning developer which I have grown to like better than pyrogallol based developers. For the Pyrocat formula see www.unblinkingeye.com.

-- Linas Kudzma (lkudzma@compuserve.com), April 26, 2002.

Pyrogallol is famous for its tanning/hardening properties - it was originally used to tam leather. In fact, pyro based developers were sometimes used to develop relief images for printing. Strictly speaking, I think its the oxidation product of pyro which provides the tanning action, whichi s why tanning is also proportional to exposure. The tanning produces two wonderful qualities to negatives. The first is a very unique adjacency effect. More importantly, the tanning prevents the developer from penetrating into the depths of the emulsion - this makes pyro/catechol developers surface developer, therefore very, very sharp i.e., high acutance. The reason for this is that developers that develop in the depths of the emulsion are typically developing irradiated grains. That is, the exposing light gets scattered within the emulsion. A developer developing in the depths of the emulsion will thus reduce the acutance of the resultant image. Surface acting developers will retain the highest acutance. This will be typically most apparent in the highlights. Small local contrast in the highlights will be preserved more accurately with a tanning developer (which is why most developers formulated for long luminance ranges tend to be based on tanning developing agents e.g., the famous Windisch formula). The reason has nohing to do with the stain but with tanning that allows even small local contrast differences in the highlights to be preserved - differences that would be lost to the reduced acutance of developers that develop in the depths of the emulsion. Irradiation in the emulsion is most problematic with areas of high exposure - so long range scenes are especially problematic and tend to be where tanning developers most readily reveal their magic. Hutchings book will provide chapter and verse on the properties of pyro. Cheers, DJ

-- N Dhananjay (dhananjay-nayakankuppam@uiowa.edu), April 26, 2002.

"..nohing to do with the stain but with tanning that allows even small local contrast differences in the highlights to be preserved" -- exactly this point is the peak of my interest now.

Linas, DJ, thanks a lot!

-- Andrey Vorobyov (AndreyVorobyov@hotbox.ru), April 27, 2002.

As an aside, a good fixer to use is Agfa FX-Universal, sold primarily for colour film but it's a good slightly alkaline general purpose fixer. Non- hardening, of course. Diluted 1+5 or thereabouts it has pH=7.3. Here in Australia it's very reasonably priced.

-- john stockdale (jo.sto@bigpond.com), April 27, 2002.