Hey everyone!

Today I want to give a free tip again. Many users may think that because development ceased on Blender Render, that it is now obsolete. While it doesn't have certain features, I really still enjoy this engine and find it surprisingly powerful when used with the compositor.

This tip is about transparency in Blender Render!
There are three types in this case and I have honestly never used the Mask one. Tried once soon after starting with Blender, but I don't really know how it works, lol. What I do know works well is Z-Transparency (Z-T) and RayTrace (RT).
This is critical, because RT supports more than Z-T does.
   Z-T is simply what you would see in office. It gives no distortion of the objects you see through it, and blocks the view entirely for any kind of fancy compositing with features you don't often use.
   RT on the other hand, is what you would use for glass, water and various other distortion effects for solid objects.

While working on a project with glass, I wanted to add volume outside and guess what, it vanished, even on RT, but, RT allows objects' material index to still show well for masking, while Z-T does not (huge difference in what you can and can't do with this engine).
For example, I have a window and I want the glass to be my masked area so I can place an animated objects' coordinates graphic on it, I simply set the material index of the frame to a value higher than 1 and use the compositor to place the texture from another render layer.
   BUT! That only works if you use RT, because we are already looking through another pane of glass. The only way, I know, to be able to get those object material indexes working behind other transparent objects, is to use RT. Remember that this does not fix all problems.
   To have a volumetric material behind a transparent object and still see it, you have to use clever masking and compositing, but trust me on this; the result is sooooo worth it, just a smidge too complex for a quick blog post, lol.

Hope this helps and have fun!

Thank YOU!!!!!!!!