Makes one wonder whether the same sand/grit in paint treatment was used on metal Murphy roofs when the cars were new, like the C&S boxcars of 1908-1910.
Conventional wisdom has it that C&S boxcar roofs were never painted, to avoid slippery wet surfaces, but perhaps that's just from observations of cars in the 1930s, when maintenance was deferred.
Jim Courtney
Poulsbo, WA