I'm using purple gamma changing the tone a little bit. The brush and pen pressure does everything else.

Now let's make the side reflections.

Use Lasso Tool. Make this kind of selection.

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Create a layer.

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Choose this gradient and hold your breath.

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Also apply a mask to hide the part of the effect.

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Moreover play with opacity settings.

Create 2nd edge.

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And, so on:

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Now
 
maybe the most important, if you a making the gem with such Polygon edges the reflections got to be correct.

I've used this Gradient to hide or expose my effect, my white gradient fill in this case.

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Now a little general reflection and we are done here.

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I've also desaturated my background to pop up the gem. Well this is it i hope you enjoyed and learned something from my tutorial, and I welcome you into my nest tutorial on making the stones.

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