Since I got back into mail art I do try and think of creative ways to use postage stamps to enhance the mail art by theme, color, and sometimes even number.
The planets of your solar system set issued by the post office last year are very nicely done, and have afforded me the opportunity to make some fun envelopes.
Using old wall calendar pages to make the envelopes, here are the exchange envelopes I sent out for April.
And if you're wondering why this post is titled Solar System (II), you can see my first Solar System blog post here.
I used all of the planets stamps on another piece of mail art here.
(PS: I have a bonus letter S that will show up on the blog tomorrow if you feel like checking back in.)