Just pressing the leaf in a heavy book will not help the leaf's color or structure last very long. Waxing by pressing between sheets of waxed paper works better. But I would consider coating the leaves, both sides and stem with a couple of coats of plain glycerin (get it in the first aid section of your drug store). Allow them to dry between coats and don't pick leaves that are too advanced toward decay when choosing them. Or get a really heavy lacquer hair spray (usually the cheaper ones, if you can even find hairspray in an aerosol these days) and give it a couple of coats of that on all sides, drying between coats. I would spray them on waxed paper. There is also light coats of spray matte varnish (unless you like the shiny effect of gloss) Post photos of your collection when you get it well started. Good luck.
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