Glaze Techniques 101
underglaze - as the name suggests these are glazes that go under a clear glaze. They are made from a mix of clay, colourant and water. They need to be applied to the piece using several layers to ensure the colour is detailed and vivid enough once fired
clear overglaze - again as the name suggests this is a clear glaze that goes over the underglazes to lock in and enhance the colour and to make a clear glass surface that seals the piece
glaze - a mixture of various minerals and compounds that when fired to a high temperature turn into a glass that adheres to the clay surface. The glaze is usually applied to pottery items by dipping, spraying or painted with a brush
glaze pencil - is a pencil that works much the same as underglazes and comes in various colours. Not to be confused with a normal pencil which will burn out in the firing process
sgraffito (in Italian "to scratch") - is a decorating pottery technique produced by applying layers of colour or colours (underglazes or coloured slips) to leather hard pottery and then scratching off parts of the layer(s) to create contrasting images, patterns and texture and reveal the clay colour underneath
slip - sometimes referred to as liquid clay, is essentially a liquid mix of pieces of clay in water. It normally has a consistency like thick cream when mixed together but slip may be more liquid dependent on how you intend to use it
wax resist - using molten wax to isolate where you don’t want the glaze to affect. It is a type of glaze decoration that involves the application of a coat of one glaze, then painting a wax pattern, then applying a second coat of the same or a different glaze. The wax resists the second glaze from adhering, allowing the painted design to show through
re-fired glaze - sometimes a glaze just doesn’t work for many different reasons. Maybe it was applied too thinly or too thickly, maybe the kiln didn’t reach the right temperature, maybe the glaze itself was faulty. Lots can and does go wrong in the firing process, that is part of the beauty of pottery. You don’t always get what you expected
If you find yourself in this predicament you can usually re-fire the problematic piece. To do this, first spray the surface of the piece with spray starch or sticky hair spray, this will help the new glaze to adhere to the surface. Once dry (it may take a while for this to happen - up to a couple of hours) then re-apply the glaze to the piece and fire accordingly
important: Fire your piece sitting on a bisque fired ‘sacrificial’ plate - this will catch any excess glaze run-off
