Create a new layer then choose the Eliptical Selection Marquee and while holding down the alt and shift keys, drag a circle selection area out from the middle as shown.
of the Glass you want to render. Pick a light and dark shade for it. Then select the circular gradient tool and fill as shown.
and do the following:
and fill the selected area with Black. Then DeSelect All, but stay in QuickMask mode.
from the Filters Menu. Choose a number (3) which will compress the existing crescent selection a few pixels inside the original circle. Then exit QuickMask mode.
then Create a New Layer and do a linear gradient fill between white at the top and a dark gray at the bottom.
to 'Screen' and adjust the transparency to suit.
drop shadow as shown in the image above. Note the shadow falls directly under the glass ball.
Here I used the Webdings font (letter 'i') and the same drop shadow settings....and we're just about done!
Last, I merge down the visible layers, reduce the image 50% and do an unsharp mask to sharpen it up a bit.