I have a huge supply of out-of-business Highball real rock ballast I use on my layout, but they've been out of business for years. But, IMO it was the BEST.
When working on customer's layouts and modules, I've resorted to Arizona Rock & Minerals, which is pretty good (I haven't tested it for being ferrous).
However, I found that AR&M is very dusty and will look very concrete-like if not relieved of most of its dust before using. Highball had the same problem.
So, I have a screen that is fine enough to not allow most of the ballast to fall through, but just the dust, which I use to catch the finer particles. I save this "dust" for making such things as game trails, paths, etc. on the rest of the layout.
If you're detail-oriented, and want your ballast rocks to be the correct size (and not trust what the manufacturer may be saying is "N-scale"), then you'll need to grade your ballast to get rid of oversized rocks, and undersized rocks. This is a two-screen process, but, IMO, will make your ballast look noticeably more realistic.
But, you say, what size are prototype ballast rocks?? To answer that question for myself, I took a short trip to the U.P. mainline winding up Weber and Echo Canyons with a measuring tape. I found the largest rocks to be around 2.75" at their largest diameter, some a little larger...but most of them being right at 2.5" in diameter with almost no smaller rocks. I also took photos of the ballast in daylight with a grey card in the photo so I could get the colors correct. I also found that there were approximately four colors of stones that comprised U.P.'s "grey" ballast, and that there was a reddish tint to the rails, ties and ballast rocks on stretches that had been in place for a while. On newly refurbished track, everything was sharply differentiated color-wise, with many places having the reddish tinted older track on one side and newer track on the other (U.P.'s trackage in Weber and Echo Canyons is double-tracked with center sidings).
So, I had some screen that had holes in it that were 0.017"...to filter out any stones larger than a scale 2.75", but I had to order screen that had holes of 0.014" to let smaller rocks and dust through...isolating the correct sized rocks to between 0.017" and 0.015". I got my screen through "Small Parts" who is no longer in business.
I was a bit surprised at just how much of the Highball Ballast got filtered out as far as big rocks were concerned, and even more surprised at how much dust and smaller rocks got separated. This proved to me that even though Highball Ballast was marketed as "N-scale" it was only "sort-of N-scale", luckily with most of it being the correct size. I saved both the oversized and undersized rocks for use in making off-track scenery.
I did this all back in the early 1990's, but only a couple of years ago, I found an official U.P. chart that listed what sized ballast was to be used for various types of trackage.
Photo (1) - U.P. Ballast Sieve Analysis or Ballast Rock Sizes:
Photo (2) - U.P. Mainlines at Wilhemina Pass on my old Ntrak modules using graded and weathered Highball Ballast along with Rail Craft Code70 flex:
For customers and friends, I started using AR&M when Highball Ballast became scarce, but I screened it too.
Photo (3) - AR&M Ballast on Nate Goodman's Layout using Atlas Code80 flex:
I did the same for branchline trackage, but used straight "cinders" instead of my 4-color mix for U.P. "Grey" ballast.
Photo (4) - "Cinders" for branchline trackage:
Some modelers prefer larger ballast rock size because it's more "obvious", but for the most realistic, N-scale real rock ballast needs to graded and de-dustified, no matter what the brand.
Cheerio!
Bob Gilmore
