Weathering Diesel Locomotives with an Airbrush

  • 01 of 06

    Weathering Diesels

    Proper weathering doesn't obscure details, it enhances them. An airbrush is the easiest way to reproduce the often-subtle weathering effects found on the prototype. ©2014 Ryan C Kunkle, licensed to, Inc.

    Working hard every day takes a toll on a locomotive. Even after just a few short trips over the road, dirt and dust begin to accumulate around the trucks and fuel tank. And within a few months of service that factory-fresh finish begins to disappear under a layer of grime.

    Recreating these "weathering" effects on a model is one of the fastest and easiest ways to add realism. There are many different techniques which can be used to weather a model. An airbrush remains one of the best all-around tools for the job however.

    Altering the finish of a beautiful model can be intimidating enough. Add in the fear many beginners have of an airbrush and it's easy to see why so many models retain their showroom look years into their careers on our layouts. But if you follow the basics of airbrushing you can create a variety of effects with very little effort.

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  • 02 of 06


    Prior to making it dirty, you have to get it clean. Gently wipe away fingerprints, oil and dust with a damp cloth. ©2014 Ryan C Kunkle, licensed to, Inc.

    Before you reach for the airbrush, there are a few simple steps which will ensure better results and save you more work later.

    Start by removing the wheels from the trucks. On most diesel locomotives, this can be done easily by removing the cover on the bottom of the truck. Unscrew or unclip this cover and remove the wheel / axle assemblies. Then replace the cover to protect the gearbox.

    The wheels can be painted by hand. Not only will this give better coverage on the wheels (most of which will be "masked" by the truck sideframes if left on the model) but it also keeps paint off the treads of the wheels which means less cleaning later.

    Next you'll want to protect all of the other areas you don't want to paint. This includes the cab windows. Apply painters tape to each window, trimming it carefully to size with a sharp knife.

    You can also mask other parts of the model if you want to represent new or replaced parts. Cover a few door panels or the air conditioning unit for example. After weathering, you can simply peal back the tape to reveal a fresh "repair."

    Finally, gently wash the model with mildly soapy water to remove any finger prints. Use a damp cloth or paper towel.

    After washing the model, it's best to put on a pair of disposable latex or rubber gloves to protect the finish and your hands.

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  • 03 of 06

    Fading Paint

    A before / after shot shows the dramatic effect of a paint fade. Both locos were the same shade of blue before one was faded with multiple light coats. ©2014 Ryan C Kunkle, licensed to, Inc.

    The first step in most weathering projects is a paint fade. A light fade will remove the shine and plastic look from the model. The more you apply, the older / more sun faded the paint will look.

    Applying the fade itself is relatively straight forward. In fact the basic steps are so simple it makes a great first-time weathering project. If you've never done this before, start with the step by step instruction found here. Applying the paint fade is nothing more than coating the entire model in a thin coat of tinted white paint.

    To speed things along, keep a bottle of thin flat white paint on the ready. You can then add a little tint of the base color of your model to soften the white by mixing in a few drops of color with the white in the your airbrush's jar or a small dish to customize the paint for each project.

    Like all of the steps described here, you want to build the effect gradually. Using acrylic paints, it doesn't take long for each coat to dry. You can speed the process with a hair dryer if needed. The first coat may not show much change. Add one or two more an you'll begin to see a marked difference. As soon as you reach the level of fade you want, stop.

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  • 04 of 06

    Road Dust and Grime

    bow wave
    Grime accumulates around trucks and the fuel tank and road dust is kicked up in a "bow wave" along the lower sides. ©2014 Ryan C Kunkle, licensed to, Inc.

    Next up is a dusting of the trucks, fuel tank and lower part of the carbody to represent the grime and dust kicked up as the train rolls along.

    This weathering starts with the locomotive's first trip down the tracks, so even a "clean" locomotive (or freight car) can benefit from at least a light dusting here.

    The color used for this step is not critical. The best results are usually achieved by a random mix of grays and earth tones. Just like the paint for your fades, it is helpful to keep a larger container of your "grime" mix handy for weathering. You can always vary the tone a little by adding a few more drops of burnt umber, gray, black, etc. for each project.

    Note that the paint used in each step of this process is a little darker than the last. It is not necessary to thoroughly clean the airbrush between steps. After removing one paint jar or emptying the hopper, blow out whatever paint remains in the brush into a cup or the back of your paint booth. Load the next color and move on to the next step.

    Concentrate your weathering on the trucks and fuel tank. Either an even coverage or a spotted look can be achieved and both can be found on the prototype. To get a more spotted look, spray with lower pressure and a higher paint flow.

    Don't forget the ends of the fuel tank and the pilots. A more spotty look, in streaks above the rails, is typical here as dirt and water are kicked up by the wheels.

    Another common feature which can be created now is the "bow wave" effect. This is a pattern of weathering on the sides near the front of the locomotive created by dust kicked up by the lead truck. The shape of this dirt cover is similar to the way water flows over the bow of a ship in motion. More noticeable on cab units, this feature can be found on any type of locomotive.

    To create the bow wave, move the airbrush in an arc starting at the front truck, swinging up onto the carbody and then gradually back down towards the fuel tank area. Again, build the effect over a few light coats.

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  • 05 of 06

    Soot and Exhaust

    Soot and oil from the exhaust builds up on the roof. Even a subtle layer of gray helps show the look of a well-maintained but working locomotive. ©2014 Ryan C Kunkle, licensed to, Inc.

    Next turn your attention to the top of the locomotive. Soot and oil expelled in the diesel exhaust collects on the roof of a locomotive. The weathering will be greatest around the exhaust stack(s) and often trails down the centerline of the locomotive in either direction from there, gradually lessening towards the ends.

    This soot can also extend down the sides of the locomotive. Again, it is usually concentrated most heavily near the exhaust stack. Mountain railroads with lots of tunnels and snow sheds typically take a harsh toll on locomotives and power which spends a lot of time in these territories can get really dirty quickly.

    Again, switch paint colors from the grime used on the lower body to a gray/black color for the roof. Start your weathering at the exhaust stack and work out from there. As you pull away from the stack down the roofline, pull away from the model and let off the paint to gradually taper the streaks.

    Repeat these strokes on the sides of the locomotive too as desired. Start at the top and work down the carbody, lessening as you go.

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  • 06 of 06

    Finishing Touches

    Even after airbrushing, there is room for extra weathering steps like adding these rust spots. ©2014 Ryan C Kunkle, licensed to, Inc.

    With the airbrushing complete, you can now properly clean the brush while the model dries.

    Remove the masks and replace the wheels.

    Additional subtle effects can now be added to complete the model, from fuel streaks below the fill cap to rust spots or other details. These can be added with alcohol pens, drybrushing, or powders. While the airbrush produces nice effects quickly, mixing different materials and techniques can further enhance the final product.

    If you haven't already done it, now is a good time to darken the recessed areas of grills and fans as well.

    After you've weathered your first locomotive, you'll see what a tremendous difference it can make. Consider doing multiple units at the same time to save even more time as you make your locomotives look like the hard working roster they are!