Moersch Tanol Speed: more on pyro developers (June 16, 2009)
Developers based on pyrogallol, the so called pyro developers or more common today PMK developers have a somewhat mythical status. On the positive side, the sharpness, latitude, dynamic range are noted. On the negative side there are aspects like toxic chemicals and the unpredictability of the staining process. The basic idea behind these staining developers is the fact that with an increase in silver density the pyrogallol builds up a layer of dye with a color that can be greenish but also red-brown. This dye will fill the holes between the silver molecules and will smooth the grain impression. This is a valuable property for very high density areas in a negative where over exposure will produce grain clumping. Edge effects improve the sharpness impression and the highlight separation will produce prints with a finely differentiated tonality, reminiscent of the fine art prints with large negative sizes.
Staining developers are often placed in the context of medium and large format photography. But the 35mm negatives can be developed in pyro too. The only problem is the control of contrast. The advantages of pyro shine in situations with a high contrast. Due to the staining action lower contrast negatives look quite dull and need a very high contrast filtration to get a decent print. With an automated system like the Heiland Splitgrade System printing is easier and more fun, because the period of experimentation can be reduced considerably.
The Prescysol EF formula I used in a previous test gave excellent results, but the shadow densities were a bit a the low side . Moersch Chemie in Germany has a different formula based on pyrocatechol and claims also a different colour of the stain. For this test I used Tanol Speed and Tmax 100.
Effective film speed
The Tmax100 film did kill the famous Kodak Panatomic X that was rated at ISO32. Kodak claimed that the Tmax100 offered the same fine grain and sharpness with a higher speed of ISO100. In most developers the true speed of the Tmax is closer to 64 than to 100 and for really good shadow detail it is often best to set the exposure meter to EI = 50. In most situations this level of shadow detail is not present and a full stop under exposure is no problem. For this test I used EI = 64 on the Gossen Mastersix meter. This speed can be fully exploited with the Tanol Speed developer.
The density measurements of stained negatives with a normal colorblind densitometer are a bit unreliable because of the color of the stain, but as a starting point they are quite useful. below the graph of the Tanol Speed shows a truly excellent curve, very close to what the Zone System demands. The base + fog is D=0.20 and the Zone I with a D=0.11 is very good, much better than what you get with the PrescysolEF developer.
Note that the Tanol/Tmax combo delivers a useful dynamic range of nine stops, much more than the current state of the art of the high end digital sensors in top class cameras.
The grain is quite small, but not invisible. The smoothing effect is there, but only in the highlights, in the shadows and mid tones there is some grain to be seen at bigger enlargements (+10 times).