Helen Scarth

But strangely
enough, of all my pre-1900 machines and all the ones of this style
including two other later Singers, 1877 and 1881, this machine is the
only one with non-magnetic slide plates.

I don't have anything further, except to note that the only Singer history I
have ever read--portions of David Hounshell's "From the American System to Mass
Production, 1800-1932"-- says that in 1866 "[c]ast iron and cast malleable iron
still predominated for parts of the Singer machine, which consisted of more
than one hunderd pounds of cast iron and only about eight pounds of wrought
iron and steel." There is no mention of brass components. By 1870 the machines
were made both in New York City and Galsgow, Scotland, with the main U. S.
factory moving to Elizabethport, NJ in 1873. In 1870 127, 833 machines were
produced.
Frank Morrison