Create a new file: File> New. I made mine Width=400, Height=400 pixels. Create a new layer and use the Selection tool to create the outline of your object. I made mine an Oval like in my Oval Interface.

Click the 'Channels' tab and create a new channel. Make sure you still have your object shape selection visible. Fill this selection with white: Alt-E> L, White. Then deselect: Ctrl-D.
Now use the Selection tool to choose any areas in your object that will be hollowed out or indented. Fill with Black. Control-Click the channel then save the selection: Select> Save Selection.

We need to makes sure the edges are smooth. Ctrl-D deselects everything. Then do a Gaussian Blur: Filter> Blur> Gaussian Blur> Radius = 3. Ctrl-L brings up the level adjustor. Notice the 3 triangles under the levels window? Drag the left and right triangles towards the middle one until the object edges are smooth.

Control-click Channel 4 selects all the white areas of the channel. Do a series of Gaussian blurs Radius 10 , 6 , 4 , 2 , 1. Then Ctrl-D to delselect and do one more Gaussian Blur Radius 1.

Select> Load Selection - the one you saved a while ago, Click the Layers Tab. Click Layer 2. Fill the selection with a color, texture, or gradient. Ctrl-D Deselects. Use lighting effects: Filter> Render> Lighting Effects> Texture Channel = 4, and there ya have it! .