There were magazine articles about micro-reticulation/grain clumping in the late 80's and 90's where the writers had done test and shown it occurs. However I think other parameters like the combinations of developer/film, stop bath, fixer and water used all play a part.
There can be very sudden & unexpected changes in tap water temperature where cold water sits in a pipes next to a hot water pipe, or warms inside the pipework in a house, then a huge drop as fresh water is drawn through from underground pipework. It is a problem in my UK darkroom but here in Turkey the water seems to hold steady to less tahn +/- ½° C even on a day like today where it's 39° C outside.
Ian
There can be very sudden & unexpected changes in tap water temperature where cold water sits in a pipes next to a hot water pipe, or warms inside the pipework in a house, then a huge drop as fresh water is drawn through from underground pipework. It is a problem in my UK darkroom but here in Turkey the water seems to hold steady to less tahn +/- ½° C even on a day like today where it's 39° C outside.
Ian
Based on his results he had to have been doing something very wrong and/or the pudding is in the print itself.

), but the whole issue of modern emulsion hardening, "grain clumping" and "micro-reticulation" needs, I think, some authoritative, professional comment.