http://alanhettinger.com/tutorials/specular/specular.pdf

There are many ways to do glassy buttons... or glassy globes or whatever you want to call them...The trick is getting the white 'reflection patch' to correspond accurately with the gradient of color below it.

The apparent shape of the glass object comes directly from the shape and size of the reflection patch.

http://skins4.wincustomize.com/JairoBoudewyn/dock/trillian_5_jpg_big.jpg

^Example^

These objects are not truly 3D, but appears to be so because of the 'shiny area' and the darkness/lightness of the color 'beneath' (inside) them.

Once you get the idea, play around a bit and see what works best for you.
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