I have two costume cards that I was going to scan, and when I was scanning them something came up suddenly. I forgot about them and now the bottoms of the two costume cards are warped. They were in a 9 page sleeve, so I place them in toploaders and put some heavy books on top of them. Anyone have any tips on how to unwarp, if it's possible?

i did see a card flattening 'machine' on the web recently that had what looks like perspex between screws so you could tighten them flat. i think someone makes them originally for yugi cards but they should fit anything

Moisture and weights. I suggest moistening a paper towel very lightly and placing that over the card that's on top of a clean sheet of paper and placing some heavy books on top, let it sit for about 2 hours. Do not wet the paper towel just very lightly dampen.You may transfer the texture of the paper towels to the backs of the cards so you can replace it with a clean sheet of bond paper. I suggest using a clean dish washing sponge, not the kind with soap already in it. dampen the bond with it and lay it over the back of the card and add weights. I do this to flatten out my sketch cards before shipping them back and used to do it for my larger watercolor paintings.

I've got a card flattening machine but she's down the supermarket at the moment.