The answer might be in the different thickness of the Tri-X emulsion compared with T-Max or Tech.Pan. The stain from pyro developers is caused by oxidation by-products which migrate through the gelatin of the emulsion; that's how it masks grain to such an extent. With a thin emulsion the stain can't spread very far, but with a thicker coating such as Tri-X's, it may spread enough to give a soft-edged image.(posted 9014 days ago)Knock the PMK on the head for Tri-X and stick to good ol' D76.