1. Similar to the gems covered elsewhere on the site, orbs have a glassy quality and are perfect for buttons, components of larger images, etc.
Start with a blank canvas; I'm using 400x400. Make a dark grey (about 80%) circle in the middle by using the elliptical shape tool whilst holding shift and making sure its rasterized, or fill an elliptical marquee in the same way, then deselect (ctrl/cmd + D). Use a gaussian blur (Filter || Blur || Gaussian blur) with setting of 1.
An optional drop shadow can be added, using settings similar to these:
2. We want to leave the edge pixel or two a dark colour, so to do this hold ctrl/cmd and click the layer that you are working on (most likely labeled Layer/Shape 1) to select the circle, but not the drop shadow. Go Select || Modify || Contract and enter a setting of 1 or 2 px depending on the size of your image. This means what we do will only effect the selected area until we deselect.
As you've probably guessed, these orbs are created with liberal use of the airbrush tool. Use settings similar to these:
The area in the top right should be dark, and the bottom left a light grey as shown in the example image. Using the smudge tool and gaussian blur (Filter || Blur || Gaussian Blur) may help - remember it doesn't need to be too neat, use the example opposite as a guide for the effect your aiming to achieve.
3. Add a small elliptical highlight to the top left of the image as in the gems tutorial, and you're done. You can play about with the airbrushing in the middle of the orb for as long as you like, I'm not too happy with the example here.
