Painting shining gems is a very easy way to boost your models. The method is very easy once you have understood the mechanism, well the trick honestly, to paint a realistic gem. In this tutorial I'll explain you how to do that.
In order to to show more clearly every passage, I've painted a gem using Photoshop. I've chosen to do that to have a clearer and sharper image, step by step. This thing (the pictures I mean) would have been harder to do on a 32 mm model because of the size. On the top of this article you can see some examples of painted gems, painted by me of course, on real models. This method works greatly on flat 2D surfaces too, so you do not need to have a real 3D sculpted gem.
Ok, so the very first thing to do is to understand where to put the lights and the shadows in order to obtain an effect of refection/trasparency and thee-dimensionality on our stone.
Let's take a look at the image:
Let's image a source of light coming from the top of the gem. The light will focus on two zones: on the top in the so called "spot of light" and and on the lower zone of the stone. On the top zone we will have the maximum direct reflected light and in the lower zone we will see the "filtered" light of the gem because of its geometry and its trasparency, so this reflected one will be less intense and will get the color of the stone.
Take a note that the light, on the contrary of what you may think, in this case increases going on the bottom. The opposite happens to the shadows. Anyway it's all shown in the previous image.
Ok, let's start painting for real. I've chosen to paint a green gem so let's make an uniform base of Dark Angels Green (Caliban Green now I think), from Games Workshop.
Now, let's work on the lights lighten the lower part of the gem. I've added a small quantity of yellow to the green to get a brighter color. You could also use a tone like Scorpion Green.
Note one thing: when I've highlighted the base of the gem I didn't paint a crescent like shape in the lower zone of the stone. This thing helps to emphasize the convex geometry of our object. Just look at the finished gem image to understand better what I'm saying.. you will see a "U shape" shadow area on the bottom...
Let's add more and more yellow painting smaller and smaller zone step by step. Note how the painted area looks like a crescent. To get a better effect try to leave a kind of darker oval shape on the higher zone of the gem.
Keep adding more and more yellow and paint into smaller areas.
Now you can clearly see the yellow crescent in the lower zone of the stone.
The lower area of our gem is finished. Let's star to give depth to the shadows of the higher zone. Add a little bit of red to the pure green (Dark Angels, do you remember?) and paint the shadows. The red color works because it's the complementary of the green.
When the mix of green and red starts to become too brownish, add some black color and keep shading into smaller areas.
The gem is almost done, just one little fundamental thing is missing: a spot of light. Take some pure white and with your brush add a little dot on the top of the stone, not too close to the boundary.
If you want you could add more lights on the lower part of the gem, it's up to you.
The gem is done!
In this guide I have showed you a very typical instance of stone: oval shaped gem with zenithal light. Of course you can use the same process for every kind of stone or crystal glass. Anyway when I paint miniatures I prefer to put the light slightly on one side. This effect gives, in my humble opinion, more dramatic nature to the model.