I had a curious experience last week. I printed a picture on Ilford FB warmtone and toned it in Kodak selenium 1:9 so I had a strong color change. I washed it properly and allowed the print to dry. I mounted it on acid free museum board using Seal dry mount tissue and set my Seal dry mount press to about 250 degrees. I sanwiched the print between the board I was mounting it to and another board on top. When I pulled the print after 3 minutes... all my tone color was gone! The print went back to a neutral gray.
Anyone ever see this before?