I've tried it on both (also glasured ceramics) also on other thicknesses. When I measured the same thickness there was the same decrease of Transmission. The higher the thickness the lower is the difference between with immersion oil or with no Immersion oil.
Hey :)
I measured the transmission of blue visible light (350-550nm) through lithiumdisilicate ceramics with an ulbricht ball and an spectrometer. The light source was a led dental curing unit (bluephase style). The light guide was positioned direct on the ceramics.
Now I wanted to test...