diXACTOL Ultra

Pictorial Planet

Barry Thornton's
diXACTOL UltraTM Two Bath

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Available in my shop

XACTOL UltraTM is a pyro (catechol) tanning and staining developer formulated by the late Barry Thornton. It was his second developer of the diXACTOL range being a much improved formula over the first diXACTOL and adding the word "Ultra" to the name to show this lineage. It provides very sharp negatives and high stain, good contrast, and long tonality.

Negatives that would be impossible with conventional developers print with fine graduation and much less struggle in burning and dodging.
Barry Thornton
The main improvements to the developer were a boost in film speed to around box or 1/3 stop under box improving shadow detail and also an increase in beneficial staining over other pyro developers. It still maintained its signature sharpness, giving an almost 3d look, and good contrast but the tonality, for me, was also improved with longer and richer tones.

Formulated initially as a 2-bath developer the instructions later added its use as a single bath. This is because, as a 2-bath some people suffered from uneven development especially around the edges of the film that touched the developer reel. This, Thornton said, was due to contamination of the developing reels with previous chemicals and/or the local water supply. Using the developer with a new reel (unused with other developers) helps and using the developer as a single bath alleviates the problem completely.
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Thornton later recommended single bath development with semi-stand, reducing agitation to every 2 minutes while extending development time by around 10%. This he said gave results at least as good or even better than the 2-bath.

  • I personally use a developing reel dedicated to Dixactol Ultra and do not have the issue with two bath.
  • For zone system work I use it as a single bath with regular 1 minute agitation. I find, because of diXACTOL's strong tanning of the emulsion, this developer makes beautiful, crisp, high acutance negatives with normal single bath development.
  • I rarely use minimal agitation finding that regular development gives superb negatives of great sharpness and lovely tonality.

Pyro Developers: Pyrocatechin vs. Pyrogallol

Thornton formulated the pyro developer with pyrocatechin because of the stain colour and the tanning. He'd used PMK, a pyrogallol based developer and although he liked it found the highlights, especially on multigrade paper, lost contrast. He remarked it was like printing the highlights with a softer grade filter. This is because pyrogallol gives a more yellow stain, the same colour as the soft grade filter with multigrade papers. This soft filter effect was more in the highlights because that's where most of the yellow/green stain with pyrogallol is formed.

He knew of a different form of pyro, called pyrocatechin, from his career in newspaper printing, and knew that pyrocatechin gave the most tanning of any developing agent.

He also said the stain colour on negatives made with pyrocatechin was mainly brown with only a hint of yellow/green. This was advantageous in the darkroom with VC papers, as compared to pyrogallol, because the brown was a similar colour to VC paper safelights therefore creating an advantageous masking effect in the highlights not the soft grade filter effect like the yellow colour of pyrogallol processed negatives.

2-Bath Development is diluted 1+19 A and B

Single Bath Development is diluted 1+7+300

I already tried it with Fp4+ (120 format). The negatives came out perfectly. I have used exactol in the past but with dixactol … i am really astonished … the detail and sharpness of the negatives.
Dirk Van Damme, Belgium
I have to say the negs are printing beautifully and the front to back sharpness on the FS3 is astonishing […] So Dixactol will be my go to developer from now on.