Beyond (or in addition to) Chalk.
Once you get fairly comfortable with the chalk, you're going to find certain weathering patterns that will require a different medium to produce what you see. The use of paints as a weathering medium - a truly broad topic indeed. I have discovered that there are as many ways to weather with paints as there are paint colors and types available.
There are several ways to apply paints when weathering:
* Washes - Basically thinning the paint to different consistencies and applying with a brush or an airbrush.
* Dusting - Almost like applying chalk, but using the airbrush.
* "Straight from the bottle" - Using a brush, piece of wire, etc. and full strength paint to produce scratches, heavy streaks, paint outs, graphics. etc.
* Drybrushing - Using a brush with most of the paint blotted off of it to produce highlights, streaks, etc.
Let's break them down and play with them.
Washes.
Typically, when you "wash" something, it means that you're attempting to clean it. We're gonna do the exact opposite. In the context of weathering, a wash means to apply a paint that has been thinned - usually to a water-thin consistency - and applied as a, well, a wash. For the most part, there's not alot of "method" involved here. After all, if you're driving along a dirty road during a rainstorm, the mud doesn't land in predetermined spots on your vehicle. It goes everywhere. It might accumulate in greater ammounts up under the vehicle, but it certainly isn't restricted to just that spot. So it is with locos and railcars.
The key to simulating these effects on models is to build up several washes using different colors to achieve the desired effect. following each with a shot of flat clear finish. Once again, experimentation will be the best teacher here.
On any given project, I have used over a dozen different washes using different paint types, colors, consistencies, application techinques, etc. I'll use a small brush for rust washes on trucks and couplers or a 1/2" wide brush (or even an airbrush) to apply a wash to the side of a boxcar.
Paint types. For the weathering on my Oakway loco, besides chalk, I used a combination of acrylics (Polly Scale and Testors Acryl - sometimes mixed together) with water, alcohol or Acryl thinner, Floquil and regular Model Master with laquer thinner and oil paints with turpentine. All these different paint/thinner applications came in handy. One type of weathering couldn't have possibly produced the results that I was after.
A few "rules" here regarding paint/thinner types. Water has a great deal of surface tension, whereas, laquer thinner, turpentine and alcohol flow very well. In other words, while water has the tendency to bead up on a surface, the others will flow freely along ribs, inside corners, crevices, etc. If I need to thin a water based paint, I'll most likely use Acryl thinner, alcohol or even Micro Set or Sol instead.
Recently, I learned of another thinning medium for the water-based types of paint. Windshield washer fluid - the blue stuff that you can pick up by the gallon at any convenience store, dept. store, etc. for next to nothing cost-wise. Brian K. passed this one along in a post on the Intermodal list, and he learned of it from a gentleman by the name of Jay Styron. You would use it just like you would use Acryl, water or alcohol. Evidently, the flow characteristics are wonderful and it's safe for the paint, decals, clear coats, etc. While I haven't tried it yet, with what I've heard about it so far, I will be very soon.
Dusting.
As above, it's almost like applying chalk, but utilizing paint and an airbrush instead. It's also more permanent than chalk, so a little thought beforehand will be helpful. And while using the dusting technique will yield similar results when using chalk, dusting will enable you to lay on a more consistent layer of grime, crud or film than chalks. For example, creating diesel exhaust residue on the top of a loco or on the side of a tractor trailer, mud/grime spray on a boxcar and rusted brake dust on the slope sheets of covered hoppers - any place that you're after a nice, even coat of "yuck", nothing beats the airbrush.
A good airbrush is the key. Take a look in the "tools" section of the site for more airbrush info. Basically, you want a gun that will produce an exceptionally fine mist of medium. Nothing beats an internal mix gun here, preferably a double action model. For vessels (to hold paint in), I'll use color cups and jars. When I get into a weathering mood, my arsenal consists of both Badger guns, the 200 with the medium tip and the 150 with the fine tip. I'll have two color cups and about a dozen jars clean and ready as well. I'll also have about a half dozen jars filled with laquer thinner, water, Acryl and alcohol for cleaning guns between different color changes. As a beginer, start out with a few jars, one filled with the thinner that's compatible with the paint that you'll use.
What paint will you use? It's all up to personal preference. I've had good results shooting both acrylic and solvent based products. They both have advantages and disadvantages. Water based products will tend to pool up more than solvent based ones will, but I've found that water based ones will produce the same effect with less paint. Solvent based products mixed with laquer thinner will set up faster and will clog the gun less than water based products will. The pigment in solvent based products is also finer than with water based products, although, as technologies with water based products continue to evolve, this won't be a factor for long. I suggest that you experiment with both - your experiences and preferences might turn out differently.
Once again, dig up that scrap shell that you were practicing on with the chalks, preferably with a lighter color so that you can see the results. Mix some Black (grimy, oily, flat, whatever - something dark) color in a jar using a mix ratio of approximately 20% color to 80% thinner. Set the pressure on the air regulator at about 20 psi. Attach the jar to the brush, adjust the paint feed (needle) so that you're barely spraying liquid and, starting at a corner of the shell, make a few passes across the corner. Don't see anything yet? Give the thinner a few seconds to evaporate. If you're working in fairly strong light, you should be able to see some very faint hints of the black. Take a few more passes, let the thinner evaporate and look again. Pretty cool, eh?? Go ahead and play with the needle to feed a little more paint. Take a couple more passes. After a while, you'll begin to notice the effects. Try feathering the spray from heavy to light, in other words, start low on the shell with a very light spray and concentrate more paint as you work toward the top.
Try a different color, maybe a lighter shade like a tan (dust, mud, sand, etc.). Mix up a different jar, same ratio as with the Black. Attach your thinner jar the gun and spray a liberal ammount of thinner through it to clean it out. Hook up the tan to the gun and starting lower on the shell, make a few light passes, let the thinner evaporate and take a look. If your shell is darker, you'll probably notice a very fine, almost dusty color wher you sprayed. A lighter colored shell will require a few more passes. Go ahead and feather in the same fashion that you did the Black, this time consentrating more of the tan on the lower third of the shell and fading it out as you work up.
Study some photos of weathered equipment and try to duplicate what you see on the shell, using different colors as you go. Don't be afraid to mix whites, grays, blacks, tans and others to the different shades.
Experiment with clear coats as well. Quite often, I'll mix a couple drops of a tan of gray shade with clear to provide what could be called a "super flat" mixture (with credits going to Ed Ryan). This yields different effects - anything from a light overall dusty look to heavily oxidized paint can be simulated with this method.
More thinner notes again. As stated before, water, due to it's surface tension, tends to bead up. Even with only a few passes with a water-thinned mixture, I'll occasionally end up with small beads beginning to form. If I'm using Pactra or Polly S (I've still got a fairly sizeable hoard of this stuff), I can get away using alcohol as a thinner. If you must use Modelflex to weather, don't even dream of using alcohol with it - you're airbrush will clog immediately. Use only water with Modelflex. For Polly Scale and Testors MM Acryl, water can be used, but I prefer using Acryl thinner with both - less surface tension, faster drying times. For Floquil products, Scalecoat (I and II) and Testors (Pla and Model Masters), laquer thinner works the best. And yes, laquer thinner will eat paint jobs, decals and plastic. But applied in thin coats, it evaporates almost immediately. As long as you're not intetionally creating puddles, you'll have no problems.
Back to the Weathering page.....