A caution against running sales and specials in your newsletter. Any discounted art is often seen as “crass” by artworld insiders. If work is discounted, it is usually done behind closed doors and in a whisper. You definitely wouldn’t open an art magazine to a "SALE" ad. You wouldn’t see a classy gallery with a “SALE” sign in the window. The only time you see these is in the newspaper in an ad trumpeting the giant, three-day "MASTERS OF ART SALE" at the Holiday Inn. It just isn’t done in certain circles. Think twice about doing it yourself if you want to be part of those circles.
The other reason not to advertise sales and specials is that you don’t want to upset those people who purchased your art at full price. If they see you are running specials, they might wait until your next sale to buy your work. Or they might not buy it anymore at all.
If you still want to mention discounted art, a better idea might be to add a "friends’ discount" coupon or handwritten note to certain people on your mailing list. This will make them feel special—like they’re "in" on a secret.