There were several posts featured on rust on this blog. I focused on mainly different techniques to simulate rust; now here are some photos I took over the years as references.
It’s worth looking over how thin and thick metal rusts, how something that was left outside without being disturbed gets dirty, rusty and gets colonized by vegetation, and how objects that are constantly being used outside for a prolonged period look like in contrast. Also worth looking at fading effects by the sun on metal and plastic surfaces, and how leftover grease and oil looks like on rusting metal parts.
It’s a kind of reference library, for myself mainly. (I’m collecting all the relevant photos into one place.) May be useful for others, too.
Of course we can talk about how real tanks never got to this stage: they were either knocked out, or were constantly under maintenance; however this is a philosopical discussion. As modellers we try to tell a story with the models we build (or not); and the overdone weathering is one way to do it. Alternatively others might do it because it looks cool. Regardless if we try to stick to the reality, models would look much more boring, so that is one very good reason to add wear and tear.