I thought I would post this to give a little bit of an insight on my weathering mediums, and perhaps a few tips. Also how I got into weathering to begin with.
I guess it helps to be a railfan for decades, observing what the prototype looks like, and from working on the prototype and seeing cars and locomotives up close. It also helps to take slides or photos of the prototype to use as reference. There are also great websites for prototype photos of both rolling stock and locomotives such as http://www.rrpicturearchives.net, which is a resource I tend to use. Whatever the source, it’s good to have a reference photo on hand of the car you’re replicating, or a similar car.
As far as weathering mediums, I tend to concentrate on only a few now. I’ve tried quite a few mediums, including watercolor pencils, but never got good results in earlier weathering projects. They may work for others, but not for me. I used to use chalks long ago as well, until I found Bragdon powders, which I still use occasionally. They have, along with powders by AIM, have a self-adhesive quality. The more you rub these on, the more they stick. I really only use these powders now on couplers for a rusted effect, and this sometimes on top of a rust colored wash.
I discovered the medium of pan pastels right when they first came out, tried them, and love them. They have a quality all their own. They go on easy, cover well, and are easy to work with. Just be careful with their use, as they are so fine, they’ll go everywhere, so have some newspaper down under your project!
The two mediums I mainly use the majority of the time now are acrylic paints, and water based oils. Why water based? Being water based, they’re more forgiving if you do make a boo-boo. They’re also easy to work with as well. You do however have to dull coat each layer of weathering you apply. Another advantage of acrylics? They’re inexpensive, plus they, along with oils, are available at any craft store. One other advantage is the wide range of colors.
For sealing everything, I used to use dullcoat liquid by Testors. This product though you really have to use carefully, as imo, too heavy a coat can ruin a model. Dullcoat in a rattle can is really not the way to go. The medium I love to use now instead is matte varnish by Vallejo. This product is a milky, thicker product that thinned with water goes on very smooth and even.
Btw, all of my weathering is done with an airbrush, or at least the base coats. I then apply as many coats and mediums as needed to get the desired look. I started out only using powders applied with sponges and brushes, but nothing beats having an airbrush. Best investment I ever made. However, shop around for the equipment you need. I first purchased a full set including a spray booth, airbrush, and compressor at a discounted price. The airbrush and compressor both however turned out to be inadequate for the job. I pretty much immediately had to purchase a better quality airbrush and larger compressor to get the job done. Another important piece of equipment to invest in is a commercial grade respirator. Whatever paints and sealants you use, be sure to protect those lungs!
Finally, I use two more mediums which for now I’ll keep a secret. Last but not least, accurate, prototypical weathering takes time, an eye for detail, and patience. I’m not a believer in weathering in a day….