I've done milk, and oil too.
Besides the fact that you probably shouldn't do oil (clogging the pores), I learned my lesson about 5 years ago.
I was expecting company, so I wanted to shine the leaves of the shefflera. I did, then took it outside to give it a good watering. Normally it can handle direct sun for a short amount of time, but not when it is slathered in oil! I ended up giving it a sunburn, for which it never really forgave me.
