The developer uses Pyrogallol, the second oldest developing agent ever used (after gallic acid). It became very popular in the late 19th century until displaced by the ubiquitous Metol. However, pyrogallol has two main advantages over metol. These are:
1. An oxidisation stain created by Pyro, which becomes a natural filter to tame highlights and ease printing
2. Tanning or hardening of the gelatine emulsion which both protects the negative from damage and reduces developer movement through the emulsion creating higher beneficial acutance
in the image. This acutance is produced even when rotary processed in a jobo or other constant agitation tank.
These two benefits are enormous when done right; and the hunt for a way to use Pyro has continued for over a century. 510-Pyro claims to have achieved not only these two benefits (as PMK did in 1991 right?) but also the Holy Grail of photography, ultra fine grain with high sharpness. I want to add yet another additional benefit for me, a single solution stock (no mixing of A, B) and it keeps for years.
That's a long list of impressive claims so maybe it's time we looked at DeFehr's 510-Pyro more closely and gave it a run for it's money against the big boys of modern staining developers PMK and Pyrocat.Formula
Formula for 510-Pyro stock:
TEA (Triethanolamine) 75ml
Ascorbic Acid 5g
Phenidone 0.375g *
TEA to make 100ml
* Updated from the original 0.25g of phenidone by Jay DeFehr "To optimise the three way relationship between pyrogallol, ascorbic acid and phenidone"
Use 1+100 through 1+500 with water.