Thanks, Hedd. I shut down Blender and my PC and brought it all up again (it's 4 in the morning here - can't sleep) and now it all works. Must be a Windows/Blender 4 Windows thing: in Linux, the behaviour appears to be a bit more predictable. Unfortunately, I'm running Blender on the Windows machine (for Poser Pro 2012 - this might change, though) and my Linux system is a laptop with a GT 230 graphics card which doesn't do Cycles. :sad:

I finally used your find: those procedural wood textures.

It appears there is a Bagginsbill of Cycles materials... the developer of this material: Wesvdes. His focus is on maths: he apparently developed this using some fairly sophisticated formulas (well, they would be to me: he probably thought the task mundane and simple). I'm hoping for a tutorial.

Monterey/Mint21.x/Win10 - Blender3.x - PP11.3(cm) - Musescore3.6.2

Wir sind gewohnt, daß die Menschen verhöhnen was sie nicht verstehen
[it is clear that humans have contempt for that which they do not understand] 

Metaphor of Chooks