The Evolution of Exactol: How I Created My Special Monochrome Developer

PHOTO Techniques, July/August 2003

By Barry Thornton Back to

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My childhood friend Peter Stott and I used to find trouble together, and I distinctly remember when Peter (who would eventually become an atomic scientist at Britain’s nuclear research center) and I filled an aluminum cigar tube with explosives and clamped it to a tiny, four-wheeled toy. While he lit the fuse, I photographed this momentous event with a crude box camera.

Usually, I took my 127-size film to the chemist for developing and contact prints, but this time Peter had another idea. In his bedroom lab he mixed a concoction of several chemicals with water. We blocked out the room light, looped the film through the chemical solutions in a dish, and wow! Negatives of our rocket car! Then he mixed more chemicals. With a red bulb in the light, we contact-printed the negatives and watched the tiny prints emerge in the home-brewed developer. Magic. I was hooked. The picture was blurred, as you would expect with the 1/60 sec. exposure. My plan was to find how to make things sharp by freezing motion—impossible with my box camera. I studied Kodak, Agfa and Voigtlander camera catalogs, but all these cameras were beyond my means.

Years went by. One night, my boss invited me to join him on a visit to his camera club. I was re-hooked, but now, I could afford a “real” camera. A Hong Kong company made the Halina 35X, an economical 35mm camera. Even with only four shutter speeds, it looked the part—a bit like a crude Leica—and its triplet ƒ/3.5 lens actually performed okay when stopped down. Camera club members insisted that large or, at worst, medium format was necessary for real quality. The rebel that I was—and still am—set out to prove 35mm could match them. At least now I could freeze motion at 1/250 sec. for non- blurred pictures. I started shooting with Agfa Rodinal and Agfa IFF slow film because club members insisted that slow film gave the sharpest results—a myth that continues today. However, I couldn’t get the same sharpness and clarity others achieved with larger formats. So, I began searching for a magic developer.

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The quest for high definition

If I couldn’t get large format’s smooth rich tones, I could at least have high definition—still not a bad approach to 35mm. Forty years ago I used D-23 because it was easy to make. It worked well, with fine grain, good speed, and I could use it diluted for increased acutance. But it wasn’t really high definition—it was similar to diluteD-76. The high level of sodium sulfite in the formula had a relatively big solvent effect. The thicker emulsion films of those days (unlike today’s straighter-line characteristic curve types) were easily overdeveloped causing ungraduated blocked highlights. Leica Photographie in 1937 revealed that Heinrich Stoëckler’s classic metol two-bath developer effectively counteracted this problem. Very soft working with a borax activator bath, it yielded superbly fine grain and almost automatic subtle gradation. Definition was good, but not bitingly sharp. I was convinced that metol held the secret; it was very fine-grained, and was initially a surface working developer. I found its edge effects could easily be exaggerated for an extra crisp look. Willi Beutler proved this with his classic high- definition formula that still works well today (try it with TMX). But fine grain it isn’t. It relies on a highly dilute metol solution with a vigor- ous activator (sodium carbonate) to compensate for the drop in developing agent volume. Sodium sulfite levels were dropped radically to reduce the solvent effect. However, tonally, the results were a little flat because of its highly compensating action. Incidentally, I confirmed that Geoffrey Crawley’s FX1 is the ultimate metol high definition developer (along with several mutations), but I don’t use it because of its similar tonal limitations. I began to experiment to find something between Stoëckler and Beutler, and the two- bath route was attractive. A two-bath Beutler formula worked okay, but offered no great advantages. I changed to sodium metaborate for the activator bath (about twice the alkalinity of borax) and experimented with increased amounts of sodium metaborate up to 20 grams per liter, while simultaneously reducing the metol content in varying amounts from Stoëck- ler’s five grams down to 21/2 grams, and the sodium sulfite content to 50 grams per liter. I experimented with various combinations of these three chemicals, and also tried all the proprietary high definition developers.

Success…and then they change the films!

Just when I had the optimum balance, they changed the films! Old faithful Ilford FP3 became FP4, a new thin-emulsion film with enhanced acutance that directly competed with Kodak’s Plus X. FP4 was advertised as “the sharp one,” and Ilford used one of my photographs in FP4’s brochure to prove the point. The photograph, a portion of a half frame negative, was taken with my Olympus Pen FT with its standard 38mm lens, and processed in my special developer.

However, as films continued to evolve in this thin emulsion/exaggerated acutance direction, the old two-bath formulation didn’t work as well. It was as if the emulsion didn’t absorb enough Bath A developing agent for activation in Bath B. The negatives became thin and flat. Either, I had to increase the activator’s amount/alkalinity, thus increasing grain, or I had to increase the amount of metol developing agent. I chose the latter, and increased the amount of metol as the films changed, until it actually passed the original Stoëckler five-gram level.

Then came T-Max, which was clearly radically finer-grained. Its 100-speed grain looked similar to a conventional 25-speed film. Unfortunately, it didn’t have the apparent sharp- ness of the conventional emulsions. Resolution it had, with lovely smoothness, but apparent biting sharpness, it didn’t.

I tried modifying my metol high-definition, two-bath formula. It worked somewhat, but the apparent definition still wasn’t up to conventional emulsions. The film’s high sensitivity to development time changes also meant that rollfilm, with its lack of exact development time for each frame’s exposure circumstances, needed a method for taming TMX’s bullet- proof highlights.

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Making the switch from 35mm to rollfilm

My film changed from 35mm to 120 as I began using my Rollei SL66. This young 35mm evangelist had mellowed, accepting the inevitable quality improvement of medium format. “Metol will have to bite the dust,” I reluctantly thought. Interestingly, I noted that Kodak’s T-Max devel- oper and Geoffrey Crawley’s FX39 developer both opted for something else—phenidone.

Like my father and grandfather, my career was in newspapers and the printing industry. My father once told me about the blackened nails of his hard-bitten chief photographer who continued to tray-develop 4×5 film in pyro, much to the amusement of his younger staff who relied on deep tank D-76 processing. The chief photographer insisted that pyro’s yellow stain and emulsion tanning gave his press camera’s 4×5 negatives extra quality.

I played with pyro, starting (like most people) with Edward Weston’s modified ABC formula. I wasn’t impressed—it didn’t look

Making a two-bath catechol developer

From my printing and graphic arts work, I knew the qualities of catechol. It had the greatest tanning effect of any developer on the gelatin film emulsion. I thought its simulta- neous tanning of the highlight areas in a neg- ative would be valuable in taming TMX and other hot highlight films. Photographers, like Ansel Adams, already used catechol when ultimate compensation was needed.

That wasn’t all. The Windisch formula—another classic high-definition film developer from the ’50s—exploited the outstanding acutance of the catechol developer, and also stained brown between the film grains for a grain masking effect. I wondered if I could make a two-bath catechol developer. I’d have the automatic highlight restraint of tanning, plus split development. With this self- limiting effect, I thought I could have a developer with similar times for all films.

I didn’t know what I was starting, and it took years to find an answer. Halfway through my experiments, I learned of Gordon Hutchings’ superb PMK formula, and used it for a picture in my book Elements. I highly recommend the PMK developer.

Why didn’t I give up on catechol and stay with PMK? Mainly because I’m stubborn and determined to complete what I had started. I knew catechol had some special qualities that would provide a different look.

In PMK, film stain is very strong providing a high grain masking effect. However, the stain varies in color and intensity with different films, tending towards yellow/green. Like any staining developer, the stain is greatest in the highlights. When printing on graded paper, the stain acts as extra highlight density, giving a more contrasty print than the negative’s density would suggest. However, with VC papers, the stain color acts as an automatic highlight-softening filter, as if you printed that area with a soft VC filter. With extreme highlights, such as windows in an architectural interior, that is a benefit. But the flattened highlight tones often look muddy, when there should be a gleam and extra separation.

Catechol does not create as much stain as pyro, even though its tanning and acutance-enhancing action is superb. Its brown stain, as well as its printing effects are consistent. Catechol adds printing density proportionately more to the highlights for both graded and VC papers, which means less actual silver development is necessary. Thus, definition is further enhanced.

It was easy to make a two-bath catechol developer. Refining it to maximize the stain was not as easy. I was able to do this by carefully balancing two activator chemicals, instead of just one, in the B bath. The definition was biting.

Working with medium-format film in the developer gave me wonderful negatives that printed superbly (35mm didn’t work as well). The grain from the coarse-acting catechol was visibly crisp. PMK uses metol for much of the development process to lower the prominence of the grain, although it’s far from ultra fine. Unfortunately, catechol needs a higher pH solution than pyro to work, which causes fog when used with metol.

Blending glycin with catechol

I solved this dilemma by using glycin blended with the catechol. Glycin, although expensive, is very clean working, even at high pH. The trick is getting the right proportions—too much gives nice fine grain, but lowers the stain level; too little boosts the stain and the grain.

When I achieved the optimum blend of glycin and catechol, I discovered that this was a two-bath developer in which most films—except ultra fast emulsions and ultra slow Technical Pan—could be developed together for the same time. The definition was startling, and the tanning/divided developer highlight restraint meant that gradation in even the negative’s densest parts was beautifully printable for subtle gleaming highlights that didn’t look flat on VC paper.

In the early ’90s, I began using this developer more for my personal work. I called it DiXactol (pronounced Dye-Zaktol). The ‘Di’ meant two bath, and ‘Xact’ represented the high definition.

It didn’t stop there. I knew glycin had special abilities as a “stand” developer used to avoid streaking. This unagitated developer technique gave the utmost highlight restraint and edge effect enhancements. I wondered whether DiXactol could do this as a single bath developer. It could, providing even higher acutance, tanning and stain.

That was fortunate. People attending my workshops asked me for the developer. At first I gave it away, but later began to sell it. I’ve never had the slightest problem with this developer. However, scattered users occasionally reported problems with streaking. This developer used as a two-bath is very fussy about water and processing equipment cleanliness, but it wasn’t as fussy as a single bath developer with partial “stand” development, and this became the recommended procedure. However, grain in small formats can still be prominent, and some older films (like Verichrome Pan) give high base fog, which requires a special developer modification. I thought I could do even better. I discovered that if I put just the right tiny amount of phenidone into the “A” solution, and changed one of the two “B” activator solutions, the phenidone would do a lot of the development. Phenidone “triggered” the catechol to increase its image stain, while significantly reducing base fog and stain. The resulting solution, Exactol, is the nearest thing to a perfect developer. It has DiXactol’s tanning and stain, but doesn’t quite have that developer’s ultra definition. It is still bitingly sharp, providing a medium fine grain that is fully usable with any format. This developer consists of 1 part of A concentrate: 1 part of B concentrate: 100 parts of water.

The “triggering” effect of phenidone enabled me to modify the original DiXactol to work even better as diXactol Ultra for ultimate definition and tanning. I rebalanced the Exactol A formula, and changed the B activator mix for the formulation TechXactol, tailored to Technical Pan for those who use ultra slow films. The tanning action holds this film’s high contrast in severe check, gives a new crispness, and provides a little increase in speed. Thousands of DiXactol users worldwide (solutions are available only from are changing to Exactol. I now use it for my personal work.

Is it perfect? Of course not. TMX and TMY work well in it, but need extra time above the standard eight minutes. It can be used as a two-bath developer as well, but the solutions don’t last long that way. I still reckon Peter Stott would be proud of me!

Moving on to Digital

In the time since I’ve formulated Exactol, I’ve moved from traditional to digital printing—mainly by Piezography. The learning curve I experienced—including the special monochrome techniques and resulting workflow—are covered in my self-published book, Elements of Transition. I researched what made an ideal monochrome negative for scanning. There is a nasty phenomenon called grain aliasing that exaggerates grain when the negative is scanned. This is a significant problem. At first, I thought the answer would be to use an ultra-fine grain developer.

This was wrong: all scans need some sharpening, usually with an unsharp masking filter. The softer definition produced by the ultra-fine grain developers means a stronger application of this filter, which exag- gerates grain. It turns out that a negative from a moderately fine grain developer (like Exactol or PMK) requires less post-scan sharpening. This means less grain exaggeration, and the stain between the grains registers on the scanner to help “smooth” the resulting file. Tanned/stained negatives scan beautifully.

About the Author

Barry Thornton
Barry Thornton’s career began in typography and graphic design, and he later went on to pursue filmmaking. Thornton worked briefly as a newspaper and printing group CEO, and in 1992 penned Elements, a best-selling photography book in the UK. He led Ilford’s “Master Class” program workshops, and formulated specialized developers and processing solutions.