A bit of history here .... Back in the old days, the AAU would not allow "posing oils" in its sanctioned BB contests. Sweating was OK but you could not use oil of any kind.
So a few of us found out a way to do it .......
Here was the solution.
About three hours before the weigh-in/contest (back then the weigh-ins were held immediately before the event and there was no prejudging) you'd hop into a hot shower to open up your pores. Then get out and pat dry and apply a thin coat of baby oil mixed with oil of wintergreen. Then pat dry once again in order to make your skin look completely oil free.f
Then we'd hit the scales and relax because as soon as we started sweating just a little bit during the mandatories - all the oil would come out of your pores and highlight the muscle.
ANd all the while the judges would merely think, "That guy sure sweats a lot!"
But no need to play that game today as most anything today is legal and appropriate.
Other tricks we used were tennis balls taped behind your knees under heavy Levis during squatting contests (Odd Lifts in those days) would give you another advantage against your less than observent competitors.