The Federal Forensic Associates report on the Davy Crockett letter almost purchased by the state of Texas for $550,000 concludes that the document was produced much later than the 1836 date written on it. An examination of the ink revealed the presence of high amounts of calcium and magnesium: "Although these materials can be present due to environmental exposure, the abundance levels are more indicative of treatment of the exhibit [the letter] with chemicals normally used in the deacidification process employed by conservators to impede the acidic action of Iron based inks on paper. ... The presence of both Calcium and Magnesium indicate the use of multiple processes, either in conjunction with each other or at separate occasions. The routine use of Magnesium was not found until the 1980's with the introduction of large scale decidification equipment for the processing of many books and manuscripts in a timely manner."
The report concludes:
"Chemical examination data is consistent with deacidification processing of the exhibit by more that one process or on more than one occasion. The combination of these factors indicates that the exhibit was processed for deacidification within a relative short time after preparation of the writing. Given the availability of these processes, it is unlikely that the original writing would have occurred during the time frame represented by the date appearing on the exhibit.
... The exhibit contains many points of concern relative to the source of paper, treatment of the exhibit, and condition of the ink line. Although we can not eliminate all possible scenarios regarding the preparation of the examined exhibit which would account for these results, it is the opinion of the undersigned that the most probable scenario is the preparation of the exhibit at a more recent time, within the twentieth century, with the subsequent processing for deacidification."
Everett Wilkie adds: "The report also notes that the sheet has a stationer's mark showing a train and reading 'Holyoke Co.' That alone would have been enough to debunk the idea that the letter dates from 1836 since the Holyoke Paper Company wasn't founded until 1857." The report, after noting the presence of the stationer's mark, goes on to say "Even though a further study of this image is outside the scope of this report, it may provide additional information regarding the timeliness of the paper."
So, in short, the letter was probably produced sometime in the late mid- to late twentieth century, written on paper made - at the earliest - around 1857.