24 years of viz experience. I am relatively new to TM but not to many other render programs. Why can I not change the opacity of a material without an alpha channel within the texture?

[anonymous_user_756deb70]

If a material comes into TM from Revit such as curtains or a mesh chair back, why do I need to boot up Photoshop, change the material to a Tiff with alpha channel or a png just to get a little opacity on that material? Is it possible to use a jpg texture and simply add a little opacity to it in TM? I'm not trying to add a specific opacity map, I just want to see a little transparency without requiring the extra work and file creation in Photoshop.