My guess would be that it was a 66-18 that Singer made with the "Wrinkle Finish" per
http://ismacs.net/singer_sewing_mach...sses-1-99.html There were also some 127s and 128s that came with the "Wrinkle Finish" per
http://ismacs.net/singer_sewing_mach...s-100-199.html I have the 128-23 - it also has many black plated parts. Even though the machine itself is wrinkle finish, the belt guard is japanned. My 66-16; from the same time period, came with a hemstitcher and early (non-template) buttonholer.
John used Windex sprayed on to a paper towel covering a White crinkle finish machine. He let the towel absorb the gunk off. Said that any paper towel pieces brushed off nicely. I have used a product called "Color Back" on a wrinkle finish hand pinker. I liked the results.
Janey - Neat people never make the exciting discoveries I do.