Left: Ravenscrag G2928C matte on inside of mug. Right: A clear glossy. The matte needs to be soaked in the kiln long enough to make sure it develops a functional surface, especially on the bottom. Mattes are not always the best choice for food surfaces, but you can do it if you blend in enough glossy glaze to make it smooth enough not to cutlery mark.
G2928C - Ravenscrag Silky Matte for Cone 6
Plainsman Cone 6 Ravenscrag Slip based glaze. It can be found among others at http://ravenscrag.com.
There is an increasing awareness of the food safety of glazes among potters. Be skeptical of claims of food safety from potters who cannot explain or demonstrate why.
In traditional ceramics and pottery dipping glazes can be of two main types: For single layer and for application of other layers overtop. Understanding the difference is important.
How to Liner-Glaze a Mug
A step-by-step process to put a liner glaze in a mug that meets in a perfect line with the outside glaze at the rim.