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A friend of mine, viewing my latest video of operation of my Lionel Western Pacific Mikado in operation, asked whether the silvery color at the front of the boiler had some operational value, or was purely decorative. (Also, there's a silvery plate under the cab.) I didn't know the answer. Can anyone help me appear wise about this?

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The silvery color on the smoke box (front) and firebox (under the running boards and cab) represents a mixture of powered graphite and linseed oil.   It is very heat resistant, much more than paint.  Depending on the mixture, it can range from almost silver to almost black.  Some railroads also used a heat resistant silver paint on these areas.

The smoke boxes and fireboxes on many steam locomotives weren't lagged (insulated) and sheathed like the boiler is.  These areas get very hot and some sort of heat resistant coating is needed to prevent rusting.

Rusty

The smokebox and the firebox (that silvery "plate" under the cab is the side of the firebox) were intensely hot, and paints of the day - and today, also, mostly - would not stand up to the temperatures. So, to protect the steel as well as they could from rust, they (the builder originally and the railroad shops throughout the loco's life), would paint these areas with a mixture of graphite (it's carbon - so most heat is no issue) and oil - linseed was used, I think - indeed, it was an "oil paint". The amount of graphite varied, as did the color. Most RR's "graphite paint" appeared pretty much black.

The boiler proper, between the firebox and the smokebox, was insulated to improve thermal efficiency, and was "lagged" with insulating materials, then covered with sheet metal - so you are not looking at the actual boiler surface in that area.

But - while the graphite was used for protection, the color of the mix was, indeed, a "style choice" most of the time, at least to a degree (no pun intended), I would think. Also, the lighter smokebox fronts - see SP 4-8-4's, for example - were easier to see from grade crossings.

Last edited by D500

The color of the smoke box and firebox can vary wildly based on who mixed the graphite/oil. In our shop one person may use more graphite than the next so each time we re-apply it could come out a different color. I've seen many steam engines have the exact color vary after a refit or extended maintenance cycle. 

 

The greyish color is graphite. Some very dark grey to black applications may be a different product mixed with the linseed oil. On our 1897 Baldwin 4-4-0 we do not use graphite. We use Bone Black. It produces a MUCH darker coating and almost looks like black paint when it dries. imageimage

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