Lay the print that you will be using down on a piece of cardboard and trim it to the desired size using a razor or utility knife.
Trim a piece of dry mount tissue so that it is about 1/8 inch shorter than the print on all sides.
Tape the tissue down to the print using masking tape on each corner of the tissue.
Heat up a clean clothing iron until it is just hot enough that you can't touch it. An iron that is too hot causes your print to blister and an iron that is too cool won’t make the tissue stick. Test the iron's heat on a print that you do not intend to use and mark the iron setting once you achieve the right temperature.
Lay the print on top of the mount board to center it for mounting. Use a ruler to assist you in finding the center. Mark the edges of the picture with a pencil once you have centered it.
Place a sheet of protective blotter paper over the print and press the iron down on the center of the print. Do not move the iron; simply hold it down firmly for about 5 minutes, depending in your iron. The goal is to heat through the blotter paper, print, tissue and mount board without blistering the image.
Nudge the print gently to determine if it has attached firmly. If it does not move, it has attached. Note the length of time that the process took so that you can repeat this length of time on the rest of the print.
Remove the tape from the corner of the tissue, leaving the iron in place.
Slide the iron to one side of the print to continue the process. Do not lift the iron as this can cause bubbles. Continue attaching and sliding the iron, maintaing a smooth contact with the blotter paper.
Erase the guidelines that were penciled onto the board. Place the mounted print in the frame and seal the frame using the manufacturer's directions.