I came back to the hobby about 2 years ago after a 20-30 break and way back then there was Opal Medium that you mixed into the oils and this gave you a matt finish but as far as I can remember it also changed the texture of the paint, however I tried to source this to give it a try and I don't think it is available anymore, I put the matt problem onto a forum and it seems that a lot of the guys use heat boxes that they have knocked together to dry the oils out, still to try this but dont want to warp the resin lol.
TERRY