Repairing a Damaged Letter

Dear Donia,
How do I repair a damaged letter?

Thomas Jefferson letter

Q. Dear Donia,

I have a letter handwritten by Thomas Jefferson from 1792 that is split in the middle. Is there a way to restore the letter so that it is seamless? Also do you think there's anything else that should be done to restore it (For instance cleaning the dirt off the letter.)? Thanks, Shailesh

A. Dear Shailesh,

What a great piece of history to have. I am sorry to hear the paper has worn to the point of breaking.
There is nothing that I can recommend that you do yourself to repair your letter. If you want it properly treated so that it is stable again (it may not be possible to make the break look seamless, it may still be slightly visible) you will need to find a paper conservator. The conservator will be able to mend the tear and stabilize the letter overall.
The best way to find a reputable conservator in your area is to consult the American Institute for Conservation's "Find a Conservator" page. Simply put in your zip code and select a specialty (in this instance you would pick "Book in Paper").  If you have never worked with a conservator before, be sure to read the information that AIC supplies as it will make for a better experience all around. I hope you are able to find someone! 
Good luck with your project!