Recently I’ve been getting a lot of questions about custom orders, I always try whenever I can to accommodate those requests. Unfortunately glazes are one of those things that are difficult to reproduce especially from photos.
Glazes themselves are a variety of powders mixed together; the majority of a glaze is glass formed through heating silica or sand at a high temperature in the kiln. Joining this is a variety of fluxes to lower the temperature and to stablise the glaze and finally there is a colourant. Colourants are usually natural compounds powders created from minerals dug from the Earth itself.
These are all held in suspension in water and when a bisqued pot is dipped into it the pot absorbs the water and on the surface is left the powdered glaze. Unlike mixing paint it’s difficult to tell how a glaze will turn out because how it looks in the tub is different to how it appears once fired, without testing it first you just don’t quite know what will happen. Even well used glazes need regular maintenance to keep its colours looking bright.
Atmospheric pressure inside the kiln or the presence and absence of oxygen will also make glazes appear differently. As oxygen is burnt up during the firing process if you limit it’s supply inside the kiln this has an impact on what you take out of the kiln at the end. You can also add a spray of ash or salt while the kiln is firing too to give a metallic finish.
Another thing which deeply effects a glaze finish is the clay body itself, I use stoneware but you can also colour stoneware bodies using iron and there are even black stoneware clay bodies sold by valentine clays. Some glaze elements on porcelain look so different – for example flambe glazes turn out vibrantly grassy green instead of deep red.
Stoneware glazes have a particular look to them and in trying to reproduce glaze finishes it’s often very difficult. I often think that a glaze is a huge part of a pot, unfortunately once a lid smashes through use you’ll never be able to re-create the way it once looked. It is changed forever.