I just grabbed a plain white envelope and started playing. First I collaged on some bits and pieces that looked interesting, then I think I put a coat of gesso over some of it to mute it a little. Then the rest was pretty much all done with Inktense pencils. They behave just like watercolour pencils when you're using them, but when they dry, the colour is permanent, hence the reference to ink in the name. You can even go back and add new marks over top and if it's dry, the stuff underneath won't move. The permanence is nice because you never know what's going to happen to that envelope between here and there. If it gets soggy I don't want the address to slide right off the front, the mail people have enough challenges.
To make the lettering stand out, I gave it a white highlight with a Sharpie paint pen, and then I used a T5 toner grey copic marker to shade the grey underside of each letter.
Then of course, stickers. I'm all super fancy up in here! Oh, but since stickers are considered cheating, (whatever), we'll just call it additional collage. If you send me a letter and it has stickers on it, I promise not to judge. Ha!
I know it says "SECRET" but there wasn't much in there that was very incriminating. (Or maybe there was. I'm not telling.)
Hey, you should go send a letter. Then you might get a letter back, and that could really make your day. It always works for me.