Chrome plating begins to appear on machines from around the 1920's onward, whereas machines made in the 20 years before this are more likely to have nickel plating. Before cleaning plated components make sure to remove them from the machine as metal polish will 'bloom' the shellac on painted surfaces, i.e. it will turn the shellac white and opaque. Use any proprietary metal polish on the plated parts, though if there is pitting, a rub with 0000-grade steel wool soaked in sewing machine oil should remove minor rust spots. Many pre-1900 machines have plated parts which have unstable and peeling plated surfaces. This is the result of poor early plating techniques and little can be done to restore these surfaces to their original condition.
Some people use steel wool to remove both the plating and the dark surface of the underlying steel.
They then polish up the underlying steel. This is effective but the resultant unprotected steel surface will be prone to rust and finger acid. Others have tried having parts replated with mixed results. An effective way of improving rusted plated surfaces is the electrolytic cleaning method. This is useful where the preservation of the patination is important as on valuable antique machines.