Reflections and glow
For a glow effect I use the standard Soft brush on a new layer, with Opacity set to between 20 and 40 per cent, and make soft dots where I want highlight to glow. I don’t overdo this effect – less is more. On the same layer I use the Path tool to draw some reflections on the crystal ball. I convert the path to a selection and fill it with white. Once I make a layer mask, I’m able to control the Opacity by painting either black or white in the mask.