Barabe hit the books, looking for other studies on early Egyptian inks. The study of Egyptian marriage certificates and land documents from the Louvre proved to be the clincher.
That study found that contracts in Egypt in the mid-third century were written in lamp black ink, in the traditional Egyptian style. But they were officially registered in the traditional Greek style, using brown iron gall ink.
The Louvre study findings suggested to the teamthat the presence of both inks was consistent with an early date for the Gospel of Judas, Barabe said.
What's more, the Louvre study found that the metal-based inks from this time period contained little sulfur, just like the ink on the Gospel of Judas.
The discovery gave the researchers the confidence to declare the document consistent with a date of approximately A.D. 280. (Barabe and his colleagues caution that this finding doesn't prove beyond doubt that the document is authentic, but rather that there are no red flags proving it's a forgery.)