In this guide I will attempt to show how I paint my gemstones on miniatures. Its probably not the best or easiest way but hey it works for me.
1. Paint the Gemstone with Black
2. Paint the Gemstone this time with the colour you want your gem to be - I have used Dark
3. Add White to your basecoat colour -D.A Green in this case and paint the bottom half
of the gem with this mix - try and maintain a downward curve at the centre of the gem.
4/5/6/7/8 Continue adding White to the mix and painting a "U" shape in the bottom half of the
gemstone each time leaving a little of the previous colour mix showing towards the
middle of the stone.
9. Paint a small thin "U" shape of pure White on the very bottom tip of the gemstone and
also a small White dot in the upper centre of the stone.
10. Paint Gemstone with Gloss Varnish
See pictures for reference and colour chart showing the colour progression through the stages. Hope this helps. Happy Painting.