There is an approximative method of dating iron gall ink:
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But I'm afraid it is out of question because it seems somewhat destructive.
Anyway I had a few other thoughts about this floating around. I cannot claim a) that my understanding goes far enough to say this would technically be possible, b) that the cost & effort would be worth a try and c) that this hasn't been discussed before.
This all is more or less based about what I read about proofing authenticity and dating / locating of the materials of the Nebra Sky Disc (yes, at first of all it had to be proven that it is not "fake")
- Natural radioactivity in the iron oxide components of the iron gall ink
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not heavily refined iron should contain Pb-210, a radioactive isotope of lead with a half-life of 22.3 years. Mined iron ore usually consists of a lot of by-materials, including oxidized iron.
"(...) when no radioactivity can be identified at all, it is a certain conclusion that the metal under examination is older than about 100 years."
Alas, here we could slowly
grow out of luck, given the timeframe for ruling out a "modern day" forgery.
Note: this is NOT about C-14, but simply measuring the remaining radioactivity in the compounds. I don't know about the amount of testing material necessary.
Side note: the conclusive paragraph of the article is very informative about "The effort required for a forgery".
- Source of the raw materials
This is about locating the origin of used source materials via isotope fingerprinting of trace materials, lead compounds etc. and referencing them against comprehensive databases of mining history and correlating them with knowns of trade history regarding trade routes & market places. In turn this can help narrowing down dating.
For example, the copper ore source of the alloy used in the Nebra disk was exactly located to a specific deposit on Mitterberg, Salzburg (the reference database contained 50.000 entries of mines).
The source for the gold alloy was found to be identical to ore of the Carnon river, Cornwall.
The method can be applied to pigments found in color compositions, like the Lapis Lazuli in Egyptian Blue was identified to come from mines as far as Afghanistan (for a nice diagram of pigment use see here: You are not allowed to view links.
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I believe the method may also be applicable to iron oxide sources used for iron gall ink. The samples are there, the isotopes seem to have been identified. IMHO it would be almost impossible for a "modern day" forger to source material that would be identical to medieval sources.
While I can't help the feeling that the purpose followed in this thread is to "put a stop the modern forgery hypothesis", I would like to think that the outcomes of such research would help the greater cause, overall.
As said, I would very much appreciate an experts opinion on this.