While I was really happy with how the wood colouring of the 3D printed flat wagons turned out it should be obvious that the colour is really only suited to newly planed wood and that in use on a railway unpainted wood wouldn't stay this colour for long. The advantage of having 3D printed the wagons is I can easily print some more and paint them in different states of repair. I currently have some more on order but before they arrive I thought I'd do some experiments to work out how I'm going to represent wood in different states of ageing.
When I ordered the first set of wagons in the finely detailed material I also ordered a set in the cheaper material I've used before for printing OO gauge wagons. While these didn't turn out well enough to be useful as models, I thought they could form the basis of a useful set of painting experiments. It is worth remembering though that as they are made from a different, much rougher and more absorbent, material that the final wagons will look slightly different.
I had two approaches I wanted to try. Firstly there was Iain's suggestion for producing a silvery grey wood colour and then a dry brushing based method that I'd read on a forum that I thought worth trying.
I started with a variation on Iain's suggestion; the variation being that I didn't have any Humbrol #27 in my paint box so I substituted Model Color's London Grey (#70.836) which I believe is a 50/50 mix of black and white. So I started with a layer of London Grey, then a thin wash of black (Model Color 73.201) before dry brushing on some Tamiya Gun Metal. I also dry brushed on a small amount of khaki (Model Color 70.988). You can see the result on the left hand model. This seems to work quite well, and I would never have though about using a metalic paint to add the aged effect. I might need to experiment with both the base grey and the amount of black wash, especially as in reality it looks a little darker than the photo, but it looks pretty good.
The second approach is similar in that there is a base colour, a wash and some dry brushing but there are quite a few more paints (all Model Color) involved. I started by painting on a layer of black (70.950) and then once that was dry a layer of khaki keeping the layer thin enough to allow the black to give slight variations in the finish. I then used the black wash (73.201) to detail the gaps between the planks etc. and to tone down the khaki. A round of dry brushing then followed using khaki followed by brown sand (70.876) and finally dark sand (70.847) which confusingly is a lighter colour than brown sand. I then retouched in the details by adding a very thin watered down layer of the black wash. The final touch was then a very light dry brushing of dark sand to lighten the raised areas ever so slightly. Obviously the effect and colour is very different to the first approach, but then it represents a different stage of the wood ageing. In fact this approach seems to match quite well with my next door neighbours unpainted fence which I think is around 10 years old.
Of course I'm not sure how well these approaches will work on the other material, but hopefully another bunch of models should arrive from the printers next week some time so I shouldn't have too long to wait to find out.