The problem is not quite grain, but small pin-prick sized white dots - particularly noticeable in the shadows. The dark shadows don't have nearly the same smooth tone as do the mid tones and highlights.

Other than that problem, I'm getting decent results with a digital negative on Pictorico with an Epson 4000 - setting are premium glossy, 2880, no color mgmt. Chemistry is from B&S, equal amounts of PT PD and Ferric Oxalate solution 1 and 2, all at room temperature. Chemistry is roughly 2 months old, but the problem has been there from the beginning. Coating is by glass rod, single coat. Developer is Ammonium Citrate at room temperature. Paper is Arches Platine and I'm printing on the top surface (I tried, accidentally, printing on the other side but it was clearly the wrong side).

I've tried humidifying the paper, but no change.

Any advice would be appreciated.