Beautiful paint job!!
Unfortunately there is not really a lot out there regarding videos. Most of them seem to airbrush an uniform darkness over all and everything. I don't like that. Here is a video, that I think is of good use.
https://youtu.be/2rYqQH_iBm8
Washes play the trick for O-scale. We have much better details and these are more visible due to the bigger surface compared to HO. I personally airbrush some brownish dirt very lightly over the lower part of the model, having all components completely disassembled. I weather the boiler, tender, all trucks and drive mechanism separately to assure good access.
I modify the light and well diluted spray (acrylics) with alcohol and the brush. You can modify the dirt where you want it and create streaks.
Weathering the black locomotive color is most difficult, I find. It is a harsh contrast for everything you bring onto it and all subtle effects can easily be overshot.
On the basic brown I then add some greyish washes, I will try to seal the first wash against the second by giving it a thin coat of Krylon Crystal Clear for future projects because you also activate the first wash when manipulating the second.
I burnished the side rods a bit and that helped to tie them a bit more to the overall appearance.
I practiced this technique on a HO model but it did not look so good. That method is really good on bigger stuff, though. If you ask me, weathering by airbrush only is not for our great scale.
You also might find some good content on the Brasstrains website. They have a video with weathering with Jerry Spolema and Juan Zuloaga. It gives a bit of an idea of what could be done but is not really a how to.
https://www.brasstrains.com/vi...ema-and-Juan-Zuloaga
Kind regards
Sarah
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