Thanks for the links. At a glance, the arnold standard surface looks like maxwell’s bsdf, but less flexible, less organised.
I think it’s worth saying, that for the majority of solid materials there is no need to worry about technical terminology. The way the user builds those materials is merely visual, by layering some spec above a diffuse base or blend of diffuse bases.
For dielectrics and IOR metals the technical terminology is appropriate.
Earlier I mentioned polished stone, You said we are limited to one layer per substrate (physically correct), but using multiple spec components is typical of most materials. So Bella’s material system is incompatible with the way everybody builds materials.. I don’t understand the usefulness of the layer system. I assume I can stack additive conductors to build up spec, but where is the fresnel/ND control?