Black Gunk – What is it?
What is that black gunk and where does it come from? I did some
Google searches looking for answers, but did not find many. In a
couple of cases, people have taken track to a laboratory to see
what this stuff is. One analysis reports
a
lot of oxides of nickel are present. A different forum post, which I
can no longer find, found evidence of bits of dead skin cells. Dead
skin cells might sound surprising until you realize that household
dust consists of a large proportion of dead skin cells from the occu-
pants of the house and their associated cats, dogs and other pets.
My testing found that strong organic solvents are the most effective
against “Black Gunk”, so this does fit with the origins of the “black
gunk” being organic material.
Wanting to see where the black gunk was coming from, I grabbed a
length of unused flex track, which was surprisingly dirty considering
it had never been used! I gave it a good cleaning so that I knew we
were starting out clean. I then wrapped one end of it in paper tow-
els, to keep stuff off of it but still allow air to get to the rails. Then I
put it up on the shelf and left it there for a year! I did peek at it oc-
casionally, and what I found after one year is that the covered por-
tion remained perfectly clean, the uncovered portion had a good
layer of easily removed white dust on it, but there was no black
gunk and no apparent oxidation from being exposed to air.
I have some spur tracks on my layout where cars are pushed, but
locomotives seldom venture on to them. I have noted that these
sidings develop much less black gunk than the active tracks. These
findings support the idea that it is the combination of the electrical
current and the rail/wheel interface that creates the black gunk. In
the absence of either, it will not form.
I am going to make some wild speculation: electrical arcing occurs
between the wheels and the rail, and the arcing oxidizes the rail
and degrades the dust into black gunk. (As an aside, nickel silver
rail does contain nickel but there is no silver in it! It is a type of
brass with added nickel originally called German Silver developed
for making cutlery that wouldn’t tarnish). The rail is formed by roll-
ing and forming wire stock progressively until the correct profile is
achieved. This leaves some oil residue on the rail from the rolling
process, which explains why new rail is a little dirty.
Calgary Alberta, Canada, where I live, is very dry with almost des-
ert-like conditions during the winter months. This results in the
house occupants (myself, my wife and three cats) having dry, flaky
skin during the winter, and consequently there is a lot of dust in
the house. We fight this dust in the house constantly and I fight
dirty track on my layout in the basement all the time. If you live in a
more humid environment, your dust may have a different composi-
tion. It would be interesting to hear from others to see if they have
similar results with cleaning track.
Brent recently retired from work-
ing as a production analyst with
Shell Canada. Since retiring, he has
taken on the role of editor for the
Calgary Model Railway Society’s
publication “The Order Board.”
He also belongs to the Bow Valley
Model Railroad club.
Brent’s other hobby interests
including oil painting, and he runs
an art school in Calgary. He enjoys
hiking and cross-country skiing in
the mountains outside Calgary with his wife of 33 years.
Experiments with track cleaning - 7
MRH-Jul 2014
