I believe that the use of 'additives' to assist swing is used widely in baseball.
Whether this is legal or not I have no idea (flipping rounders - girl's game
We used to mess around in the nets with 'Lipsol' (a type of lip gloss, a small smear of which on the flannels would assist shining of the ball). The big giveaway was the bright red smear on your thigh, because it dissolved a little of the colour from the cricket ball's cover.
Has anyone noticed how the new balls used in the current test series swing like crazy, even with both sides shiny?
I think the ball they are using is the 'Duke' as usual, which has the emblem and loads of gold paint on one side only, so it's already pretty unbalanced.
After 10 overs the swing tends to die down, then gets going again after 30-40 (conventional swing). There wasn't much evidence of any reverse swing at Trent Bridge, presumably because of the lushness of the outfield.