I hope this is the right group, or that maybe this will at least reach those who can help. I am working on preserving old family photos, photos dating back over 100 years ago. I am scanning them to make digital copies and then want to store them properly to keep them safe. While going through the old photos I found a letter from my great-grandfather to one of his friends whilst he was on active duty in 1918 during the world war stationed in France. It even has the mailing envelope and everything. However, the letter was written on very poor quality paper and is already deteriorating and falling apart as it was stored in it's original folded form from when it was mailed in the envelope.

Is there some sort of special adhesive spray for archiving that will help hold the paper together so it doesn't get worse? I know it needs to be stored in low humidity to prevent mold and low temperatures, but it's there a special document frame or case used to store old documents that will protect from the elements and further deterioration for many years to come? I'm not talking preserving it like the declaration of independence, within reason. Maybe something that would be less than USD$200.