Wax paper is certainly non-stick, but the couple of times Ive tried to work with it, I couldnt get it to behave. Everything went in a separate direction, greased pig style. Try this. It will take an online order and an hour or so of prep work, but just the first time. After that, everything will be ready to go.
1) Measure the inside of your boxes. Then, go to
http://www.clearbags.com/art-photo and order a size of Crystal Clear bags that will fit inside. When you get the bags, cut your mat board to fit inside the bags. Youll want a not-quite-snug fit. You dont want the mat board to slosh around inside the bag, but you also dont want it to be so tight that the bag bows the board.
2) Cut your watercolor paper to the size of the mat board. Make sure you know the grain of the paper. You want the paper to warp parallel to the long dimension, not washboard across the width. Tape each piece of paper to a plastic bag covered mat board at all four corners. Loop the tape clear around each corner so that one cut end overlaps the other. Tape seems to stick better to itself than any other surface!
3) Now, put the characteristics of the paper to work for you. Start your coating at least two inches down from the top of the paper and end the coating at least two inches from the bottom. The uncoated paper will fight the longitudinal curl of the coated area. Youve wasted some paper, but given the price of commercial liquid emulsion (ouch) its money well saved.
Also and obvious, but I'll mention it anyway: If you have the option of opening the boxes in the dark at any time during the drying, it will go a lot faster.
Best of luck and fun.
d