I know it seems as though I am stuck in the past and stuck on Singer.
Since I just started this blog, I have to get you caught up. Here is a bit of trivia for you. Yes, another Singer 15-91. But this one is different. All of the pieces that were usually shiny were kind of black looking. The serial number of this machine put it's manufacturing date at 1942. It sort of looked like what they do with gun barrels. Yea, the process commonly used by gunsmiths to provide a measure of corrosion resistance to their firearms. It was a common practice of the day for metal protection. Even the "safety razor blades" of the period were submitted to the "Bluing" process to help protect them.
The front plate, the presser foot lever, the needle plate, the bobbin plate cover, the stitch length lever, and even the foot it self , all appeared to be covered with this "Gun Barrel Bluing".
The back plate........
Even the thread spool posts.
I can only guess that this had something to do with the WAR effort. After receiving some additional information, It does appear that Singer not only made gun parts, they actually were given the blueprints and made the entire 1911A1 pistols! Several rifles were partly or completely made by Singer, enough so that they were stamped behind the Bolt "Singer MFNG".
As for the machine itself, after a good cleaning and oiling, it ran like a top. I made a sewing video for a potential buyer. Video Here
Singer probably just went ahead and threw their parts into the Bluing Vats right along with the gun parts to save money and materials. Singer was probably very proud of their part in the war effort, but probably wanted to distance them selves from "Guns" as fast as possible after the War. I'm pretty sure it didn't fit in with their Home/Family marketing strategy.
And, by the way, no rust what so ever on any of the "Blued" parts.