If you heat new screws to slightly red hot and then quickly dump them
into motor oil, when cleaned, you will have black screws that look like
antiques.  If the screws are the same shape and size you will have
difficulty telling them apart from the original ones unless you examine
them closely.  Most modern screws have shallower slots than antique
ones, plus the threads on older screws are usually sharper.  Other than
that, the average person wouldn't be able to tell the difference.

Vincent Morgan, New York City