Initial Impressions when mixed with water
As you can see above, when mixed/thinned with just water, thinned paints and glazes tend to create water marks where the colour pools and dries at the edges, while the pigments give a grainy texture if applied to an un-shaded flat colour. It is this 'grainy' property that gives the extra effect we are looking for when using them to simulate mud and soot textures.
Applying Pigment with another 'medium'
But what if we change the medium we are using to apply the pigment? Here I have taken some of the pigment in its powder form and mixed it with a watered down paint, and a painting 'medium' which will suspend the pigment and distribute it more evenly than water alone. It also slows down the drying time, allowing you to push the pigment where you want it, unlike with a wash which dries relatively quickly and cannot be removed easily.
In the above photos I have applied the brown pigment and medium, then added black pain to the mix, thinning slightly with water, then applying highlights after everything dries. As you can see, the 'sediment' quality of the pigment adds a dusty/weathered quality while at the same time giving the depth of shadow that can then be defined with additional highlights. Each of the pigment applications were one coat only, and 'feathered' into their desired location, rather than being built up layer by layer as with a glaze, wash, or through blended layers.
Applying to the whole tank
|Heavy dry brush highlight.|
|Brown pigment, mixed with Matt Medium, applied roughly to recesses then wiped clean.|
|Black paint and brown pigment, again applied to recesses and shadows and wiped clean.|
|More depth and contrast added with some black wash and line highlighting.|
So the end result is quite 'harsh' compared to my previous attempt using glazes, and allows a lot more of the base colour to show through. This is great for those looking to utilise a camouflage pattern, and is quite forgiving if any mistakes are made as it can be easily tidied up on the fly, rather than having to apply more base colour in a complex pattern. It certainly looks more striking on the tabletop!
As you may have noticed, I haven't actually used the pigments to 'weather' the tank, I have used them to shade it! The next stage is to apply the rust, mud, soot and grime that these pigments excel at. There's no real thinking outside the box here, just copy what you see in real life. Mud will be splattered on around the tracks, rust streaks down from any exposed or aged metal, and dust settled on top, kicked up from moving parts. I tend to take photos which inspire me and then copy rough patterns. If you are not confident with this then I recommend sealing the model with clear coat so you can easily wipe clean as you go without affecting the previous pigments.
In the above photo I have used the opposite side of the tank, and applied thick/unevenly mixed brown pigment to represent mud, flicking it at the lower track areas from the edge of a piece of cardboard. I also took the redder pigment from the pack I bought and mixed it with some liquid clear coat, giving it an almost transparent look. This was applied to the previously painted scratches, and to some of the duller rivets.
I plan to finish the whole tank to this level before applying the 'dust' as I may decide not to as it could obscure some of the details. In the mean time I have included a couple of 'real world' photos I have snapped which have inspired me to try out weathering. Always keep your eyes peeled for inspiration!