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I have a British 1d Penny Red stamp from the 1860s in my collection with the numerals 77 in the left and right margins. Only nine stamps bearing the numerals 77 have been authenticated to date. I am trying to determine how, or if, the original steel engraving plate was altered. I would like to know what would one be looking in terms of impression, chemical composition etc.
The stamp has undergone a detailed scientific analysis. First, through Bio-Imagery the numerals 77 were clearly identified with no other numerals in either margin. In addition, the stamp has not been tampered with any form whatsoever (all fibres are in tact).
The stamp has also been examined utilizing Electron X-ray Micro-fluorescence (EDXRF), the results revealed mercury, lead, sulphur, etc, and the impression of a numeral 1 in the margins via SEM back-scattered scan.
Given the above context, my questions are as follows: First, the original plate was made of steel—all one piece. If the original plate was altered from the original numerals 177 to 77 what would one be looking in terms of impression?
Secondly, if the mercury, lead and sulphur, etc. clearly binds to the numerals 77, but not on the numeral 1s, what type of analysis on the stamp can be conducted to show a plate has been altered?
Enlarged back-lighted details of the stamp below: