@carlso Carlso, I applaud your efforts to weather your UP Challenger. It certainly does look more weathered than the stock model with its white stripes and white tires.
However, having several dozen brass and plastic UP steam engines to run on my rendition of the Wasatch Grade between Ogden and Wahsatch, and having weathered up several brass Big Boys, Challengers, Light MacArthurs and also plastic UP steam locomotives, there are certain things that UP steam engines have in common with their weathered/dirty looks when still in operating status.
First, the colors to weather them is NOT rust or rusty brown on the top or top sides. UP steam engines were maintained by the company shops at all locations manically so their availability was considerably more than most other railroads' steam engines in the steam era. This means that if any rust formed, it was almost immediately blasted off and the surface repainted...glossy black....or glossy two-toned grey.
Secondly, UP Big Boys, late Challengers and FEF's were the icons of UP's steam power, and even though they got dirty in service, they were cleaned often...sometimes every day, with most of the engine body never getting dirty enough to completely obscure the gloss of the main color, or the light grey tone of the smokebox and firebox. When some of them got relegated to helper or branch line service in the middle to late 50's is when they started appearing really dirty.
When the fire was put out on the engines and they went into storage is when they started to rust up, the gloss disappearing from the paint and getting a more uniform delapidated appearance.
Your weathering looks like a Challenger that should be sitting in a line of other out-of-service Challengers, with windows boarded up, rusty/dusty grimed-up with the accumulated dust/dirt/pollution from the yard and engines that are running all around them...a nice, even coat of weathering, and this is because your engine is lacking some specific weathering that accompanies in-service steam engines. But, you can use what you've done to get more specific, and represent a Challenger working hard still in revenue service.
On steam engines in service, the weathering was anything but "even"...with different parts of the engines getting dirty in different ways, with different colors and textures due to grease, oil, soot and water that accumulated due to the engine working and the fairly porous nature of the lines, valves and joints that carried these dirtying elements.
The first thing to do is get online and find some photos of the prototype engine you want to weather while it was in active service. Of course, you're going to find engines in various states of cleanliness and dirtiness, but for steam engines, there are some definite areas that require more than a dusting and random application of "dirty" colors.
Photo (1) - UP 3700 Class oil-fired Challenger in the last days of helper service in Weber Canyon in the late 1950's:
You will notice that the firebox is definitely not dark, but still very light...a flat grayish aluminum color that got flatter and grayer the longer it was between paint jobs because of the heat baking it. Although you can't see it in this photo, most of the smokebox was also a similar color...which is very close to SP Lettering Gray...with no metallic sheen whatsoever.
Of course, both the firebox and the smokebox got dirty in different ways...the smokebox top being blackened by ultra-flat cinders, and the smokebox by dust/dirt and oil/grease being thrown up by the speed and rotation of the drivers in front of it.
The shiny black of the boiler was also blackened on top by the cinders coming out of the double stack...drafting was a problem with Challengers, which is why many of them got fitted with smoke lifting "Elephant Ears" up front eventually. However, although it isn't immediately evident from most still photos, the gloss of the black paint in many places on the boilers was very noticeable where the dirt, grime, soot, dust, grease, oil and mineralization didn't collect.
Photo (2) - Even with a goodly accumulation of dust, grime and soot, you can still see the glossy highlights on the domes and sides of the both the engine and tender in this photo:
Speaking of mineralization, you can see in the photo that around the steam blow-off valves on top of boiler in back of the second sand dome, that the mineralization from the hard water on most of the UP turns the black into nearly white as it evaporates off of the hot boiler, streaking the boiler as it runs downward. This accumulates on top of the side running boards, the piping and the drivers directly under the blow-off valves...and on the fireman's side...under the dynamo from the condensing steam. The steam condensing on the top of the boiler also gradually lightened up the top of the boiler, even through the exhaust soot as you can see from the photo.
The mineralization on UP steam engines was a trademark of nearly all types in all locations, although it was worse from Cheyenne to Ogden and into Idaho because of the hardness of the water, even though UP had very large water treatment plants all along with way to soften the water somewhat.
Also, because of this hard water, streaks would often form on the rear half of the sides of the tenders, usually accumulating on the rivet lines...but this streaking was a whitish grey color...not rusty or brown.
A lighter, flat warm grey formed from the predominantly grey color of UP's track ballast and the accompanying dust thrown up as the trains sped over it. This stuck to the undercarriage on the oil and grease that was always there, as well as the sideframes of the trailing truck and the tender trucks and pedestals, as well as the rear of the tender...like dust accumulates on the very rear end of automobiles too. A slight dusting of reddish brown was also evident, from the reddish brown of the soil along much of the right-of-way in Utah and Wyoming.
You'll note that in this photo, the journal boxes of the trailing truck, the tender lead truck and the tender pedestal look very light. This isn't weathering, but it's from the aluminum paint that all UP steam got on journal boxes that covered roller bearings...indicating they weren't to be oiled with waste oil rags stuffed in them like on friction bearings. You can see the aluminum circle painted on the lead truck's wheel hub centers in this photo too if you look closely.
So, when weathering a steam engine, you should use both an airbrush...or chalks...and paintbrushes. Don't evenly weather the entire engine, leaving the sides in places the original shiny black and the smokebox & firebox their distinctive colors. I paint my brass engines with enamel based paints (Scalecoat II) to look brand new, but I weather them with acrylic paints, and the water streaking is easily achieved by first carefully painting the light gray (almost white) using a thinned color in its confined area...then immediately streaking it with a fairly damp (with isopropyl alcohol) small striping brush (with long bristles), wiping downward to get the streaks.
Water from condensation, rain and water standards would also streak dust and grime on the engines, so streaking can be done anywhere using the alcohol dampened brush technique before the paint cures.
Streaks that are light can be easily made by cutting small gaps in a note card and using those gaps as a mask to spray light streaks along rivet lines. Make them not sharply defined by holding the card a distance away from the surface you're painting...the further away the card gap masks are, the more blurry the streaks will be.
Dark streaks and shiny streaks can often be seen coming down the sides of tenders from both spilled oil and water.
When you do streaks, make sure you make them straight and perpendicular to the rails. Any odd variation will be immediately visible and noticeable.
Photo (3) - Light and dark streaks on 3700 Class UP Challenger. Note some dark streaks are shiny and some light ones follow rivet lines:
Sometimes water pools, especially on tops of the side running boards and flat horizontal surfaces of the tender. To get the characteristic "pooling look" of water that's not evaporated yet, but partially gone...I use a thin concoction of alcohol and really small dabs of unevenly applied acrylic paint applied with a couple of sizes of paintbrushes. I still have a good supply of Polly Scale paints for my weathering, but I'm sure any of the new substitutes will work just as well.
Some engines got weathered in distinctive ways, such as Big Boys and Challengers accumulated road grime on the front of their gray smokeboxes in a very distinctive pattern near the bottom of the front face, forming a dirty oval there. The bottoms of the smoke boxes were also often seen to be dirty, spattered brown. Big Boys' and Challengers' jointed and swiveled steam pipes on the sides of the boilers running from the top of the rear set of cylinders to the front cylinders, turned a shade of greyish Roof Brown after cooking the paint on the insulation wrap from the temperature of the high pressure steam inside them. Also, water and oil streaks on the Challengers' centipede tenders was pretty much the same on all of them being alike in position, just differing in intensity.
Photo (4) - 3900 Series coal fired Challenger circa 1947 pretty well weathered, showing the dark patch under the smokebox front, the lighter mineralized front & rear drivers and the noticeably lighter smokebox and firebox colors:
Also note that the hubs on the leading truck aren't painted aluminum, nor are the journal covers on the trailing truck and the pedestal tender. This practice began sometime in the early 1950's. Also note that the bells on the front of Challengers and Big Boys eventually were painted black, not polished brass. Notice also that the hinged parts of the big steam pipes is a much lighter color than black...being a greyish brown.
Hope this assists you in getting a more exact idea of how to further weather your Challenger. You've got a good start, but need to get specific.
Oh, and the big hinged steam pipes on Challengers were positioned inward, not sticking out as you have arranged yours. If this causes them to lift the boiler again, it could be because the swivels on the tops of the lead cylinders are not assembled properly. My brass Challengers and Big Boys never had the problem of lifting the boiler.
Cheerio!
Bob Gilmore
