View Full Version : 510-Pyro dilution behavior

Jay DeFehr
6-Jul-2006, 16:39
510-Pyro is unique in many ways, not least of which being the fact that it is a single-solution pyro developer. Some formulators of two-solution staining developers have commented that single solution developers are less versatile than two-solution developers, and that single solution developers don't respond to dilution in a linear way, but neither of these claims are true for 510-Pyro.

The standard dilution of 510-Pyro is 1:100, which gives development times similar to D-76 with most films, but it can be diluted anywhere between 1:50 and 1:500 with very predictable behavior. Once a development time is optimized for the standard dilution, it is a simple matter to determine a development time for any other dilution. Generally, when calculating a development factor for a developer dilution, an allowance is made for developer oxidation, which varies with development technique; rotary development oxidises a developer more than semi-stand development does, etc.. In practice, one would not use the same dilution for rotary processing as for semi-stand development, so the differences in oxidation are practically insignificant in that case, and it is only when using different dilutions with a common development technique that oxidation plays a role, and even then, the factor is a minor one, and can usually be ignored with 510-Pyro. As a practical matter, I would consider 1:100 the optimum dilution for rotary processing, except in rare circumstances where a more concentrated developer is needed to build contrast rapidly, as in procesing J&C 400 for printing on Azo G2 Canadian paper, or some of the self masking UV processes, where a 1:50 dilution might be more convenient. To calculate the development time for a 1:50 dilution from the development time for the 1:100 dilution, simply divide by 2. For those developing roll films in tanks using intermittent inversion agitation, to find the development time for a 1:200 dilution, simply multiply 1:100 time by 2. I find 1:300-1:500 dilutions best suited to reduced agitation development, and an increase of 20-25% adequate to compensate for the difference between rotary agitation and semi-stand development. So, if you're getting appropriate contrast with 8min of rotary development in the 1:100 dilution, but want to see what difference reduced agitation might make, figure 8min X 5 for the 1:500 dilution for 40min., + 25% for reduced agitation for a total development time of 50min for semi-stand development. If 50 min. is more time than you want to dedicate to your experiment, use the 1:300 dilution for 8X3+25%, or 30min. These calculations are generally accurate, but will vary with class of film, water quality, and other variables, so individual testing is recommended.

These variations in dilution and agitation will allow one to process a wide variety of films, to any contrast of which the film is capable, with a range of local contrast, grain and tonalities to suit any creative end, by any processing technique one chooses, without resorting to reformulating one's developer by modifying the ratios of the A and B solutions, along with dilution, etc., etc., which makes testing an order of magnitude more complex. Having formulated my own two-solution developers, I speak from experience.

510-Pyro is very easy to use, predictable and consistent in its behavior over a wide range of dilutions and processing techniques, despite what the experts might say.


28-Aug-2006, 18:57

I've been using the 1:200 for both 120 tri-x 400 tank and HP-5 4x5 on a uniroller base.

From the above, you think (guess I'll try to see) the 1:100 would be better with the roller base?



Jay DeFehr
29-Aug-2006, 01:34
Hi Mike.

Yes, I would choose a dilution that provides a development time long enough to ensure even development, and no more. HP5+ develops to a contrast suitable for VC enlarging paper with 6:30/70F/rotary development in the 1:100 dilution. The same negs print well on Azo G3. Extending rotary development time offers no improvement in a neg's printing qualities, and encourages grain clumping and general stain. If you're getting good results with the 1:200 dilution, and the extended development time is not inconvenient, you can get by with 1/2 as much developer. You'll have to weigh the value of shorter development times vs conservation of developer for yourself, but I always opt for shorter development times with rotary processing. Good luck.