For Sale: Vintage S. R. Mitchell & Company 5 Gram 9998 Silver Ingot. $12 posted by standard post. Registered available if wanted. Prefer Paypal gift for payment. Stanley Robert Mitchell [1881-1963], mineralogist, metallurgist and businessman, established himself as a gold assayer in 1911. He founded S. R. Mitchell & Co. Pty Ltd in the mid-1920’s and operated as a major refiner of precious metals. The majority of ingots are believed to have been produced from 1970 through the early 1980’s.