Paragraph 10 F1

is wholly or mainly of gold or of silver or of gold and silver assaying in all its gold parts not less than 375 parts per thousand and in all its silver parts less than 800 parts per thousand; and

was manufactured before the year F21950 and has not since the beginning of the year 1950 been the subject of any alteration which would be an improper alteration if the article had previously borne approved hallmarks.