Lemon juice or vinegar diluted with a little water. mist onto the stock from a spray bottle. That usually ages paper products nicely.
Take a small sponge, like a make-up one, or one from a craft store. Smear it on an ink-pad, like brown, or tan,or any color really. Smear the ink on the paper in circular motions in the center and outward motions near the edge, so that the edge is slightly darker. It is a really neat effect, and you can do it once you get your paper cut down to your desired size and shape.
the ink pad methid was what i was going to suggest, too. try going to a rubber stamping website to learn more techniques to use on paper. here’s one….
I accidentally spilled coffee on a card I was working on and I liked the effect. I have used tea also. You can’t use too much. The sponge and ink works really well. They even have ink pads for the stressed look. Check hgtv.com. They have good info and online videos too.
Burning the edges has a nice effect
spill weak tea on it, or weak coffee either, brush the edges if you don’t want the whole thing colored.