MATANIM
Yes, you have to be terribly fussy to select the surface correctly in Surfaces and in Matanim (which is where I was duffing it) and close Matanim when you change the function to true. It needs a new Matanim opened and closed for each surface, which ain’t no problem for a simple surface, but can get tedious for multi-part surfaces [hope that makes sense]. Anyway, I have managed it now for a wide variety of surfaces and functions, so I am fairly happy with it. Thanks again.
PS Certainly a lot easier than Shader Mixer, although being a bit of a programming buff I got a weird satisfaction in making animated opacity work in Shader Mixer, with inspiration from Richard Haseltine’s post. SM needs lots of TLC, I think.
MOVIE MAKER
Well, I just threw that in, in disgust with Dreamlight, who pester me daily to buy their wonderful bargains, but don’t update their software!
However, using your idea with the sphere, I am already getting great rough results just with photos on my hard drive and on my copy of Carrara. Great idea, looking forward to learning more about HDRI, which always put me off before. No idea how to render HDRI in Carrara, can’t see it in the render settings, but I will sure be investigating this bigtime. Thanks for that little bonus, would never have occurred to me.
Thank you oh “Caroline, also known as Carnite” 
Regards
Ed (also known as DeadEd)