Trouble with porcelain
My porcelain is almost like flagstone; unlike the original sample, the tile is a greyed out brick red when dry and becomes the rust of the original dry sample, (as desired) when wet. Although apparently sealed, it seems to have a tooth or be almost gritty on the surface. Is there any matt or satin enhancer that can be applied to the surface that will not peel? It is in a shower enclosure. I have yet to see one that is not for natural stone applications and go so far as to say "not for ceramic or porcelain tile.
If it is truely porcelain, do not try to apply a sealer. The very nature of porcelain is that it is very hard and essentionally, does not absorb much of anything. The only porcelains that might need a sealer is if it is polished - this opens pores in the surface.