I think you have the right idea, but I'd do it using paint washes rather than actual. While there would undoubtedly be some lumps of spilled coal lying about, most of what comes out is coal dust, as Robby said. However, this dust is so fine that I would just simulate it using a wash of black paint or India ink. I think using real coal dust is way too much effort for not a lot of return.
The area immediately under the tipple would be totally black, gradually lightening as the distance increases.
Connecticut Valley Railroad A Branch of the New York, New Haven, and Hartford
"If you think you can do a thing or think you can't do a thing, you're right." -- Henry Ford
You want to use some real coal "dust" to represent this. Ballast, even "N" scale cinder is really too big. As stated, the areas around all but the newest tipples are nothing short of black which turns into a quicksand-like muck when it rains. On bright sunny days, the older coal weathers into a dark gray color all the while new dust is shaken loose from the bottom doors of hoppers and settles from the endless vibration of the crushers and screens and conveyors used to move the black diamonds. It's this dust that coats everything. Nothing works better than the real thing but run a magnet through it first, the material used in heavy media wash plants is slightly conductive which can cause some detection issues if you run a signal system. Took me weeks to figure out where the slight current draw was coming from.......
Robby Modeling the L&N CV Subdivision in 1978 http://s226.photobucket.com/albums/dd247/robby-ky/CV%20Subdivision%20Layout/
Your idea is just fine, and you could even add a higher percentage of coal and still be fine. In fact, the few coaling facilities I have seen (long ago and far away) were totally landscaped with coal - mostly small sized. Heck, even the ballast was black as it was covered with coal dust.
The thing is, the prototype steam loco (and some diesel facilities) were just plain dirty - but we modelers find it hard to cover everything with dirty dirt.
ENJOY !
Mobilman44
Living in southeast Texas, formerly modeling the "postwar" Santa Fe and Illinois Central
You are thinking correctly, IMHO. I have an Appalachian (S.W. Virginia) coal mine in HO, and have made a number of railfanning visits down into Clinchfield Country there in deep SW Virginia.
At the tipple, recognize that some coal dust and coal spillage is falling out every day or even all day every day if it is an around-the-clock operation (and before installation of more modern polution and loss-prevention controls). The surface under and close to the tipple can be nothing but accumulated coal dust and resultant muck when it gets wet.
In trying to capture the dark look of what I have seen, I use "cinders" as ballast on most all of my backwoods/shortline coal-hauling railroad. Under the tipple I have quite a bit of "coal" itself, blacker and shinier than the cinders. This coal effect then tapers off from the edge of the tipple to about two carlengths away. For the more modern coal-loading facilities I have seen, the ballast is the more standard grey, but still drifting toward black immediately around the loader.
The shading difference is difficult to capture in a photo, but is noticable to the eye.
Bill
I model N scale. I am putting in a coal tipple. For ballasting the track I am thinking I need to blend gray fine and coal cinders to give the appearance of coal dust and coal spilling over dropping out etc. I was thinking 1 part gray two parts cinder for under the tipple and immediately around and then flipping the ratio as you move away. Does this sound correct? Wanted to get some ideas on what others have done.