I purchased this Walthers 65' Thrall Mill Gondola from the famous G&G Hobbies in Northwest Indiana last year, and it has been sitting in the layout’s yard since then. This is 100% stock from the box. I whipped up some fast weathering with Floquil and Testors enamels and thinned Dull Cote using my Paasche V. I kept it simple because on my layout, this car would be relatively new, and not heavily used yet. The rusted pipes are Evergreen styrene sprayed with a custom rust juice made with some Floquil Rail Brown, Dull Cote, artist oils in: black, raw sienna, and burt umber, and pastel powders in light and dark rust colors. All of that was liquified with a large amount of lacquer thinner. This stuff is toxic, obviously, so you have to be well ventilated and wear a organic vapor respirator. I bet it can be achieved using good acrylics, alcohol, water, and pastels, with some flat finish water-based model paint. Maybe I’ll do some tests. I have been lazy about not reaching for oil-based things lately.
The pastel powders give you the texture, but because the particles are large, you need to have an airbrush with a larger needle. I have several airbrushes, so I switched to my Vega for this, which I keep configured for this kind of thing. The hot thinner bites into the styrene right away, but due to the presence of the oil paint, this stuff will take a few days to dry. I also brushed some of the rust juice randomly inside the car, then followed it up with the airbrush using the same stuff. Brushing the rust mixture works really well, but for the pipes, it wouldn’t be appropriate.
After drying overnight, I lightly brushed some pastels on a few places to give the surfaces some variability. These pipes would have been stored outdoors for a long time with the amount of heavy rust present, but also when they are touched or moved and then allowed to rust again, they show that history. When spraying the pipes, the airbrush is able to easily deliver the look of a pipe that has been sitting outdoors if you run your spray pattern along the length of the pipe, creating a different quality of rust on the side that would be more exposed to the elements. The ends of pipes may be more prone to rust due to the cut, but all of these are just thoughts in the modelers head that help direct the process, they are not accurate for every situation.
This isn’t an amazing achievement, but perhaps it is a good example of what can be done pretty quickly; ignoring drying time, the whole job probably took 15 minutes.