For example there are used when you want smooth surfaces but they can sometimes run underglazes are used.

Glazes are applied after the first or bisque fire.

There are some under-glazes that are applied to leather hard green-ware (Before the first firing) Under glazes are normally mat - not glossy

When you apply a glaze care needs to be taken to not glaze the part that will be sitting on the kiln shelf. When the piece is fired, the glaze melts and will become like a glue if it is touching or melts and runs to touch the shelf and the piece being fired.

Quite often the base of the piece is painted with a wax. The glaze can not get through the wax and if any glaze gets on the wax, the glaze can be wiped off. Be careful not to get the wax where you want the glaze. Some people will do a wax resist and have an area deliberately not glazed.

The first way to apply glaze is to dip the piece in a bucket of glaze. Let it dry and wipe the glaze off the bottom of the piece or you can wipe it off the foot. (Planning to have part of the bottom above the shelf and having a ring or feet to stand above the shelf)

Glaze can be painted on with a brush

Glaze can be sprayed on with a sprayer.

Some people apply more than one kind of glaze to a piece.

Glazes contain a clay body, a flux, a glass. They can also contain a color. The ratio is determined by how high the glaze will be fired. and whether it will be shinny or mat