Most blackening chemicals are Selenium Dioxide or a variant thereof.
Scott, if you are looking for more of a rust color, or a any sort of brownish patina, Neolube is not for you.
It will make the track more of a weathered gray or what I think of as "weathered steel".
Jax Chemicals makes a wide variety of really good metal blackeners. Don't confuse them with other
"Jax" companies. There is more than one on the net.
I have used this:
http://www.jaxchemicals.com/jaxshop/shopexd.asp?id=41It is still a blackener, but perhaps will have more of a bronze overtone you are looking for.
Check around their web page. They make a lot of "blackeners" and "darkeners". Unfortunately,
the stuff only comes in pint bottle for $15 each, and it's not cheap for them to ship it either (same issues --- hazardous chemicals).
I've only ever tried the one "darkener" I mentioned above.