I researched as much as I could online (I know, it's the internet) and all of these so called "master call makers" said to finish the inside. Without it the open pores of the wood would tend to absorb the sound vibrations so that's why I started to put it on the inside of mine.
Right, wrong, or indifferent that's what I went with. I went with crystal over glass because of the louder longing reaching call, as I already have an aluminum, 2 slates, and another pot that I'm not sure what it is without looking. Plus I just wanted to make my own.