Jennifer from A Red Pumpkin Studio (read an interview with her here, and find her blog here) makes beautiful antique paper. And she is generous enough to share with us her method:
Making antique paper is really quite simple, you just need a little bit of patience because it needs to be done in layers.
1. Use heavy paper. If you want to antique something that you have printed, print it first using waterproof ink.
2. Crumple the paper. The colours will soak into the crinkled parts for those nice long veins in the paper.
3. Cover with coffee, tea, or some combo of both. This will be your base colour. Add ink or watercolour to this mix if you want it to have a certain colour to it. For example, you can add a bit of scarlet ink to the coffee if you would like it to match red leather. Cover the entire paper.
4. Add coffee grinds in certain areas, they'll stain it darker. Add salt on top of that, it'll soak up the colour and leave lightened areas. You can also use tea leaves, watercolour, ink spots, etc. You can also press paper with non-waterproof ink onto it, which will transfer some of the colour. The more varied the things you use to colour and unevenly stain the paper, the more interesting and realistic it will be, rather than being a uniform coffee colour. It's going to take a while to dry, so leave it alone!
5. When it's dry remove all the grinds/salt etc. The salt will very likely leave little shiny things on the paper, so if you have a stiff brush (like a nail cleaner), use it to remove them. I usually put another thin layer of coffee/tea on at this point. It wets the paper just enough to get rid of the rest of the salt, and make it a little darker.
6. Repeat steps 4/5 until it looks the way you want. Try adding very strong coffee where the crinkles in the paper are so that they become really pronounced, and dripping dark coffee or ink on it from above for a different pattern to the staining.
7. If you need to smooth the paper out after it's done flip it over and iron it. You can use steam and a fairly high setting (another reason to use heavy paper), just don't hold it on any one place too long. If you have a big enough board and table you can mist it with just a little bit of water and press it flat. Use lots of books for weight and then have patience until it's totally dry!