At cone 5R pure Alberta Slip (left) is beginning to melt and flow down the runway of this tester. It is producing a matte gunmetal surface. Pure Ravenscrag Slip (right) is just starting (it needs frit to develop melt fluidity at this temperature). The iron in the Alberta Slip is melting it because of the reduction atmosphere in the kiln (it does not move like this in oxidation).
A type of ceramic glaze: Pebbly matte black. For functional surfaces, it has enough glossy to not cutlery mark and be easy to clean.