Tony's comments are spot on. Paint pigments are not UV-stable long term and so the fading seen in steam era freight cars is in large part due to the action of sunlight on the pigments (yes, there is also oxidation of the carriers, which, btw, are not always a "clear matrix", but can in fact contribute their own color to the paint. In addition, pigment molecules exposed to the oxygen in air will oxidize, particularly as any protective coating from the paint begins to break down
Since fading due to UV is due to sunlight, and sunlight is part of the weather, this fading is, imho "weathering". Now, just like the saying "all newts are salamanders, but not all salamanders are newts", fading is weathering, but not all weathering is fading.
Taking into account the fading of paint when considering the overall weathering of a model or prototype care is an important component to understanding why the car appears as it does.
From: main@RealSTMFC.groups.io <main@RealSTMFC.groups.io> on behalf of Tony Thompson <tony@...>
Sent: Friday, September 16, 2022 10:52 AM
To: email@example.com <firstname.lastname@example.org>
Subject: [EXT] Re: [RealSTMFC] SFRD
On Sep 16, 2022, at 8:29 AM, Randy Hees <randyhees@...> wrote: