Clipping Mask Techniques?

Okay.. I'm familiar with using the Clipping Mask along with splatter brushes to make clippings.. But I'm having difficulty understand how Fallen uses it. In their Fallen Angel tutorial they used the Clipping Mask to improve the quality of a render by making jewels on it have better quality. I really don't understand how they did it.. Did they like turn on the CM option then brushed red colors over the jewels in a new layer?

 

on a new layer just brush red were you want then apply the clipping mask (must be above the render layer)

 

So basically.. I make a new layer above the render, activate the CM mode then brush over where I want the effect? Or do I activate the CM mode after I do the brushing?

 

it doesnt make a difference which way you do it you will get the same effect