A while ago, I weathered a Burlington Northern PS 5277 that was submitted to Jeremy at TWS...
Within the thread for this model on The Rustbucket forum, a member proposed that perhaps I might put together some kind of video on how I drop fades on my weathered models. I'm not really one for doing videos so I thought I might break out with a mini shop here with flicks that could translate this process of mine into a clearer light that might be easier to grasp in lieu of mere vocabulary of instruction.

Please know before I proceed with the flicks, that I chose a model that was remotely similar to the BN PS boxcar that I referred to and weathered a couple of months ago. Also of note, if BN in fact rostered such an FMC combo door boxcar, the search for a proto flick of one rendered too time consuming, therefore I just randomly picked a car that I thought had good color contrast and a fade just for the mere purpose of doing this mini shop.

The model I am about to go postal on is a basic old MDC "Shake the box" kit. It's a really subpar model, detail-wise in comparison to some of today’s more modern models so I consider it as a prime candidate to whack down for this tutorial....

Without further ado, let's get on it!

1. Here is the model in its dark green factory applied paint and also a flick of a prototype that will serve as guide to achieve a color transition and fade.
Before I begin here I will display the items needed to begin this project. First of all, I employ a space heater (instead of a hair dryer) as some dudes might use. Be very cautious to never hold the model closer than 6 to 8 inches away from the heater if you elect to dry the paint in this fashion. I have had incredible success using this type of heating method though I have had a few mishaps in the past.
Next, we view all of the necessary items that will be utilized to fade the car. We have,...a cup of clean tap water, a wide soft haired brush, a small snubbed soft haired brush, toothpicks, cotton swabs,  a clean dry terrycloth towel and lastly, three different shades of Acrylic paint. Two shades of green and an antique gold. (I have a hard time calling these paints "cheap acrylics", as they are the cornerstone of ALL of my weathering projects, which would render them "extremely valuable to me ;D)...
I always begin by distributing three separate drops on a plate (pallet) of the colors I will mix to achieve the desired effect...
2. With the paint ready, I will always prep the model with a misting of Dull Cote before I commence. Not only does this preserve the factory applied graphics, but it acts as tooth to hold the brushed on acrylic colors. This happens to work very well and is a crucial step in any of my weathering projects.
3. With the car having its application of Dull cote applied, I will now take the wide, soft haired brush and saturate it with water. Then I will pick up a sufficient amount of the clean water and introduce it to the side of the three different colors of paint I will be using.
I then start mixing the three colors by taking a dab from each drop to a separate area on the plate.

When I'm satisfied with a color match from the prototype reference flick, I will keep bringing water into the pooled paint until it is VERY watery.

When I'm down with the wet consistency of the paint water ratio mix (30% paint to 70% water), I then begin to brush on the first of multiple layers to come.
I must say that it WILL look absolutely atrocious with this first wash so please don't become discouraged, the transformation of texture and color will surprise you as you continue with the next few layers.
Man, I know it looks extremely hideous at this juncture but believe me it will manifest itself in the following steps. I now take the same wide brush and clean it and what's more important, I DRY it on the clean towel so it can be used as a sponge to basically mop up the excess paint that gravity has allowed to accumulate along the lower car body.
VERY IMPORTANT: Brush stroke from the top down and do NOT disturb the downward flow of the paint on the model at this point! Let it run down and fill every bit of the car's surface. You'll just want to absorb the excess along the door tracks, stirrups, ladder rungs etc , where it will accumulate.
4. NOW, at this stage, the layer process begins dudes. Turn on the Space heater and set it on a high temp. You'll want to hold the car at a minimum of 6 to 8 inches away from the fan of heat. Keeping the car at a safe distance will prevent the thin details on some of the finer models from melting. (like I have stated already, I have destroyed a few decent models using this type of heater by holding them too close, so use extreme caution here.).
5. I don't need to explain the repetition of the same process for the additional layered applications here dudes...but I will note, DO NOT dull cote between applying the multiple layers! And when applying the ensuing coats over the initial ones, brush the new layers on with an EXTREMELY light stroke of hand, or there becomes a grave chance that you will remove the existing layers that have already been applied thus having to strip the model and start all over again. Do NOT worry about covering any of the painted on graphics at this point. As long as they are somewhat visible through the thin layered acrylics it will make it plausible for the removal of the paint that obscures them. Remember to always repeat the space heater drying method between EVERY layer. So, here we are, check out the flicks representing the point we’ve come to.
...see the color transition starting to come to life dudes?