This is a short tutorial to help show the various stages I tend to use to make colour art. I used ArtRage 5 for this, but you could just as easily use Photoshop or Gimp as the terms used are generally common.

So, let’s start.
Stage 1 – Line Art
Create a layer, call it Stage 1. Create a simple outline of the piece on that layer. Easy.
Stage 2 – Base Colour
Create another layer (Stage 2) underneath the Stage 1 layer. Select a colour. Grey in this case, and colour it in.
Stage 3 – Dark Textures
Create another layer (Stage 3) between Stage 1 and 2’s layers.
I select the Stage 2 layer, then use the magic wand to select the whole of the Stage 2 layer. Then with the selection highlighted, select the Stage 3 layer. This gives me a good boundary for the texture without needing to tidy up after.
I have a couple of textures I use for this, but use what you can find which you think might look good. I then select a darker shade of the base colour, maybe even some green for lichen effect, and dab it on.
Stage 4 – Light Textures
Create another layer (Stage 4) on top of Stage 3’s layer.
Basically, the same as the work we did on Stage 3 layer, but we use a lighter shade of the base colour, or white spots or something.
Stage 5 – Shadows
Create a new layer (Stage 5). This can be anywhere. Set the layer to Multiply, and opacity to around 50%. Use black as your colour.
Decide where the light is coming from (and stick to it going forward), and then start adding shadow to areas that would be in shadow from the light source position.
Stage 6 – Highlights
Create a new layer (Stage 6). This can be anywhere. Set the layer to Overlay, and opacity to around 50%. Use white as your colour.
Based on where the light was coming from in Stage 5, start adding highlights to all edges and faces that would receive highlight from the light source position.
Stage 7 – Engraving
Okay, let’s get funky.
Create a new layer (Stage 7), and it can go on top of all the other layers. Set it to Multiply. Use the base colour from Stage 2, and using a pen type brush write your engraving on the art.
Then we need to apply some layer effects. You will want Emboss (inside). You will need to adjust the light position, so that it correctly follows the light source decision you made in Stage 5/6.
Stage 8 – A bit of extra detail
Back to the Stage 1 layer and add some extra bits and bots for good luck.