The wonderful world of glazing

When it goes well it’s wonderful, when it goes wrong it’s anything but…
In past newsletters I’ve touched on some pottery basics – clay, turning, firing, and even glazing. But my glazing skills have really been put to the test in recent weeks as I grapple with trying to work out new methods for my current project. What might seem straightforward in the world of colour is extremely complex in the world of glazing.
The glaze is the final layer, the coating that fuses with a ceramic item in firing, intended to colour, decorate, strengthen and waterproof that item. As a rule, glazes can be classified into two types: those that are fired at low temperatures – up to 110° centigrade – seal and waterproof the clay, and are also decorative; and those that I use, fired at high temperatures – at least 120° – which are absolutely impermeable, amalgamating with the surface of the clay to improve the quality of the finished article. They also have a strong aesthetic element. I prepare my own glazes, and they are what give my pottery its unique character.
Raw glazes are compounds of silica, minerals, and metal oxides, and are applied in various ways, mainly by dipping the item into a glaze solution or by applying it directly, either with a brush or by spraying.
That might sound straightforward, but a lot can go wrong:
If the firing temperature is too low, glazing will not be uniform, and if it doesn’t fit properly, it’s like a badly made item of clothing – too big or too small. If the firing temperature is too high, the glaze will run.
If poorly applied, the glaze will blister, be uneven, and can also fail to adhere.
Incorrectly mixed raw materials can cause crystallisation or air pockets in the main body of the clay;
and lastly, there are kiln accidents – items stick together, power cuts create havoc, and small pieces of debris cause imperfections.
Essentially, patience and determination are what you need. Good work is often lost when experimenting, but when you finally get it right – it makes up for everything.

Welcome to a world of colour, the glazed kind

Glazing is one of the most frustrating aspects of making pottery, but once mastered it is also one of the most rewarding. Ultimately it is necessary to use metal oxides, stains, underglaze decoration, commercial or self-made glazes, and in some instances overglaze enamels and lustres in order to give your ceramics colour, depth and complexity. Colour gives pottery an identity that, in many cases, can be even more obvious than the identity achieved through form.
Glaze mixing and testing is complicated and often involves a lot of time and effort. Not everyone has the interest or inclination to delve into the complexities of chemical and mathematical formulae.  Most potters, even those who can mix glazes, use commercial glazes or underglazes to some extent.  What’s more, commercial glazes are also screened for toxicity, which makes them safe ‘liner’ glazes for foods.  The range of commercial glazes grows constantly, adapting to ever-changing trends and offering vibrant new colour selections, a great indicator of what the market likes and an opportunity to be brave and experiment with new colour
Decoration applied beneath a glaze in pottery is known as underglaze. Underglazes can be applied by brushing, pouring, dipping, spraying, sponging – pretty much anything goes. They add colour and depth to your work, and are ideal for detailed decoration.  Another option is to use clay slips or engobes, which are, in fact, ‘runny clays’ with added colouring oxides or commercial stains. Slips are used on the bare clay whilst it is still wet or damp, and their colours bleed into the glaze when fired.
Lastly, potters use what is known as an overglaze enamel or lustre, applied on top of the glaze and then fired at low temperatures. These are generally  used as for decoration..
Personally, I tend to use spirals or texturing as the background for decorations. I either use glazes that emphasize these details, or engobes that are actually integrated in them, and then apply a glaze that will seal the item and make it food safe while giving it an overall colour. I mix all my glazes, some from my own recipes achieved by trial and error, and others from books that I have slightly modified to meet my needs. I choose colours that, I feel, suit my shapes and look equally good on the shelf or on a plate with food. My signature glaze is, of course, my blue glaze, which I use on its own or combined with white. It reminds me of the Mediterranean Sea in spring or at the end of summer, and since I created this one myself, I feel that this colour is me, in a nutshell.