Hi.  It's been awhile since I have used Carrara and am very slowly working on a huge forest fire scene.  I have started out by using a volumetric cloud and three lights (Red, Gold and Orange) to make the flames.  I plan on doing post work in photoshop to blend things to look the way I want, but have hit a small snag.  I want to make  masks of the cloud at different transparency and settings, but don't remember how to do it.  I think it has something to do with the alpha channels, but am not sure.   Also what is the difference between: Render Alpha channel and Use Premultiplied Alpha?

Anyways here is a quick look at my progress so far.

Sincerely,

David