I am using a t-shirt press to dry mount my FB paper onto a museum (archival) board.

What I do is that I put the photo with the tacked tissue onto the board, on top of that I put a piece of baking paper and a piece of paper on top of that. Than i close the press. 85C for 1.5 minutes.

When using matt adox paper, i get strange figures on the surface because the baking paper is getting structures in the paper due to the heat and these while pressing can be seen by the eye as a more shiny area.

Is there a better way?