Not able to pull off simple combination of volume scatter and volume absorbtion: cycles I was following ben u's tutorial on Basic Volume Shading.
https://www.youtube.com/watch?v=9Ybk0qNFhqw

I was doing OK with "Volume Scatter", but as soon as I put in the "Add Node"
(3 min 46 seconds in tutorial) and then tried to add "Volume Absorption" shader, the cube turned black.



I tried this https://blenderartists.org/forum/attachment.php?attachmentid=402469&amp;d=1443634665 but, got the same result.

There must be something very basic that I'm missing but, I don't have a clue what it is.

Would greatly appreciate your help.
Thanks.
Wrong Add node

The Math (Add) node you are using works with grayscale values (on the left in the image below).

You would like instead to Add a shading to another shading: you must use the Add Shader node you can find in the Shader nodes group (on the right in the following image).



The color of the input/output socket is always a guide for the correct connection.