Some modellers like to go for the pristine out of the box look, but others, such as myself, like to weather their models. Models are usually produced ‘clean’ because it is easier for the manufacturers to do so. Adding weathering is a very intricate and time-consuming process. But what is weathering?
Put simply, weathering is the process of simulating dust, grime, and other factors such as graffiti on carriages in city models. The same applies to buildings. Some modellers prefer to use standard buildings that you can buy in hobby shops, but others will build their own. You can use cardboard sheeting or plastic to do this and you can even build certain structures out of matches.
As mentioned before, the weathering you want to apply very much depends on where your model is set. If for example, the model is a freight train in a US desert setting, then you would look to recreate sandy and dusty weathering. The same sand is corrosive to the trains themselves, so you may want to try and recreate a sandblasted look. You have to get creative and one way to do this is to actually rub sand into the paint of the model. You may also use an airbrush and enamel paints to recreate the look of dust and sand.
If you are building an inner city model, then you have a bit more of a complex job. Graffiti is not easy to recreate and the best way to do it is to look up pictures of graffiti online and then use a permanent marker pen to create your own version on the carriages. Decals are a better option for recreating graffiti in your model train station unless you are a budding graffiti artist yourself.
If you are building a steam train model, then you might want to add some blackening to the engine itself. This can be done through air-brushing or dry brushing which involves wiping a lot of the paint off a fluffy brush and then applying it to the model with quick and light strokes.