Involved. [Sam smooths a hand over her hair, aware it wasn't a very helpful answer.] You take a page out of an epistolary novel that's had every noun and verb blacked out, and you use a feather from a rooster which can't crow to write to whoever on it with lemon juice. Whoever you're addressing it to, you have to use whatever that person was first introduced to you as---might not even be their real name, doesn't matter.

Once you've got the paper addressed, you have to wet it with seawater, sweat, or tears to the point it's soggy enough to hold an impression, and stamp your message into it. The way I learned, a person used scrabble tiles; I've been using wood blocks, since I never found a scrabble set. You have to finish before the paper dries, and then shove it into a bottle, and stop the bottle up with cork. You then have to coat the entire bottle in wax, preferably white, and carve a sign [she gestures; it's a circle, with a line across the middle] in the wax over the cork.

After all that, you've got to chuck it into a river and watch it until it's out of sight. The next time your addressee goes to take up a blank piece of paper, or turns to a blank page, or opens a word processing document, or goes to compose an email or text? The message is there, until the book is closed or the window minimized.

[Like she said; involved. But, for a ritual as useful as the bottled message ritual can be... well worth it.]

Sounds busy.