The Dead Sea Scrolls Unit conserved the papyrus and documented it with the modern multispectral system used to monitor the state of the scrolls.The C-14 dating of the fragment is an important piece of evidence in favor of it being a genuine ancient artifact.
In order to confirm that the document was genuine, a small sample was radiometrically dated in the Weizmann Institute in Rehovot. The sample provided a date similar to that determined by the paleographic evaluation (based on the letter forms), thus consolidating the dating towards the end of the First Temple period.
It is true that forgeries have been made using ancient materials. But I would be surprised if there is any blank parchment from the late Iron Age II available for such a purpose.
That said, we had exactly the same situation with one of the other two First Temple-era scroll fragments. The Jerusalem Papyrus was carbon dated to around the same time. Nevertheless, Northwest Semitic epigrapher Christopher Rollston had reservations about its genuineness, based on anomalies in its script. I don't know whether that debate was resolved. For details, follow the link.
I would be interested in hearing what Professor Rollston has to say about this latest discovery. Unfortunately his blog appears to be down – or at least I can't access it.
I would now say that there is a good case that this new scroll fragment is genuine.
This article by Amanda Borschel-Dan in the Times of Israel also has new details about the process of recovering the fragment: Ingathering of the exiles? Extremely rare First Temple-era papyrus repatriated. 2,700-year-old inscribed papyrus, a letter to ‘Ishmael’ written in early Hebrew script, joins only two others from biblical times. But that’s just the beginning of the story.
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