Hello, if I understand correctly you want to adjust the transparency of an object
I'm going to change the mtl property of the obj file
is this what you're interested in?
translated google

Hi Golia,

It was a good idea but no ! [:((]

I explain :
I did that you said with the mtl file (d 0.975 ).

Directly under sh3d, Yes with a outside screenshot ! [=D>]

Look at the left side...
---------------------------
But in standard rendering...

Outside and without light, opaque propertie has disappeared.
---------------------------

Outside and With light, no difference.
---------------------------

Inside without light, no difference !
---------------------------

Inside with light, same result !

Thank you for your idea but it's not positive... [;)]