Weathering (showing signs of wear and tear) can add to the realism of any model train set, but it needs to be done carefully. One, often overlooked, important consideration is the age of the individual freight wagon being weathered. Not all wagons on a freight train are necessarily of the same vintage or have experienced the same weathering conditions. A freight train could comprise a mix of fairly new and considerably old wagons.
For example a model train layout depicting a mid 1960′s railroad might comprise mainly of wagons built around 1950. That would make most of the wagons around 15 years old.
Compare this to a freight train on a modern day railroad layout. Today’s freight train might include several brightly colored newish wagons along with a couple of 35-40 year old wagons built around the mid to late 1960′s. Weathering of the older 1960′s wagons would be different to that seen on the newer wagons.
So, always consider that a freight train is made up of several different wagons of different ages and backgrounds rather than all the wagons on a train being constructed at the same time and experiencing the same weathering conditions.