What are these used for?

[Calicat]

More info on that subject here:

Window stop bracket plates

Were these 69-70 window stop bracket plates originally painted black on back and silver on front? Seems l8e I have also seen them natural without paint, but won’t that leave them vulnerable to rust? [47427AAB-D67A-4051-BBCA-4782DB9DF21D.jpeg]