[patricka]

Depending on the value of the item you may consider taking it to a professional paper/document conservation company. I have a panoramic real photo that came from an estate sale and had been rolled for 90 years. It was very tightly rolled. I took it to a professional conservation company here in Chicago. They first placed it in a controlled humidity chamber to relax the paper and then they pressed it inbetween sheets of archival felt. Came out perfect flat with no cracking or tears. I think the key thing to consider is how brittle/tight the paper is on the one you have.