The info I am looking for is not common knowledge and not something
you can find from a google search.

No need to search when you have https://www.learning-maya.com/rendering.php
and there is still precious little info on the mental ray shaders there which is a shame.

There are these as well
https://test.jzinfo.com/bssrdf.htm
https://www.impresszio.hu/szabolcs/Me...aySampling.htm
https://www.kiaran.net/tutorials.htm
https://www.motiondesign.biz/ (do not buy this video possible fraud)
https://www.drone.org/tutorials/displ...ps_mental.html
https://www.cgchannel.com/news/viewlastnews.jsp?catID=5

I am aware of how to render with hdri or glbal illum or caustics ect
this is a request for a tutorial on mental ray shaders