Today we are going to make something like this:
II'm going to make a red one but you can do any color you want for this
Step 1: use Fire plugin (does not matter which. Just use one where it makes flames)
Step 2: Make a new layer. After you've doe that use the eclipse tool or make a shape and put it where the color you want your gem to be is.
Step 3: Use Crystallize on the fire layer. Cell size 22, Quality 2.
Step 4: go to the layer where the shape is. Use magic wand and click inside your shape. Press Ctrl+I and switch to the fire layer. Press Delete And merge the fire layer and the shape layer together.
Step 5: Make a new layer. In the new layer, draw a black curve and a white curve on each side of the gem. In the adjustment tab, use transparency on the curves.
You have a choice:
!: If you want just the gem, stop now.
2: If you want the ring, go to http://forums.getpaint.net/index.php?/topic/25078-how-to-make-a-ring-without-a-gem/