Hi Ken,

You're correct; the formula as given makes 100ml of concentrate, and I call it 510-Pyro for the ratio of pyro to ascorbic acid.

510-Pyro can be diluted over a very wide range, but "standard" dilutions could be considered to be 1:100, 1:300, and 1:500, for no better reason than the following: 1:100 gives development times within the low-normal range (5-7 minutes for most films), with standard intermittent, or rotary agitation, 1:300 requires 1ml of developer in 300ml of solution, which covers one 35mm film in a standard daylight tank, and 1:500 requires 1ml of concentrate in 500ml of solution, which covers one 120 film in a standard daylight tank. These dilute solutions are typically used with reduced agitation and extended development times. There is more specific information at the blog.

I make the distinction between pyrogallol developers and catechol developers consistent with historical usage. When pyro is mentioned in the literature, it always refers to pyrogallol, and not to catechol, and the descriptions and characterizations of pyro are not interchangeable with catechol. Catechol is chemically more similar to hydroquinone than it is to pyrogallol, and this can be confirmed by the fact that catechol can be substituted for hydroquinone weight-for-weight in most formulas without important changes in the resulting developers. The same is not true for pyrogallol and catechol. In my opinion, which is consistent with the historical literature, catechol developers should not be referred to as pyro developers, but staining/tanning developers, where appropriate (not all catechol developers are staining developers). I hope that clarifies my usage of the terms.

If you decide to try 510-Pyro, or any of my developers, please don't hesitate to contact me with any questions you might have.