LIMITED VS OPEN EDITIONS: Essentially these two are the main variations. Open Editions mean that there's no restriction on the number of works being produced. Limited means exactly what it says, it's limited. Some editions though are conceived so large that it's a bit unfair to call them limited. Though in the strictest terms of the word it's true that an edition of 5000 copies still is a limited edition, in reality it's pretty open.
Uses a clear limitation: the big ones are in Editions of 3, the medium ones in 7 copies. The smaller ones 32. For two reasons. One, all prints are handmade. Contrary to machine printing where you just have to push a button to produce a second or n-th copy, making copies in a darkroom is still quite some work. So, if Kurt has to make a large number of copies, he doesn't have enough time to make new pieces. The second reason is a respect towards the art buyer. You can argue about this, but to me, it feels more honest to give the buyer some exclusivity. I believe that a 'Kurt Deruyter' carries some kind of signature look. By limiting the series, I'm protecting both the look as your purchase.
ARTIST PROOFS: These are prints that Kurt made in the process of determining the right 'look' for the print. He keeps them for future reference and for exhibitions but it's always stated how many copies are kept, just for transparency.