Choosing the right pottery glaze for your ceramics is an exciting process and the stunning results in the end are so worth it! Choosing the right glaze will depend on your clay body, firing temperature and type of pottery you create. For example, if you create sculptural pieces the surface glaze doesn’t have to be food safe and you can experiment with many glaze surfaces. Although, it is very important to choose glazes that are food safe if your stoneware, porcelain or earthenware piece that is meant for functional purposes and is to be used for food. Ultimately, your glazes will enhance the durability and texture of your pottery and put the final, beautiful touches on your work. It can be like Christmas morning when you open the kiln to see your glazes and glaze tests!
Three main types of pottery glazes
Glazes are formulated for each temperature range low, medium and high fire glaze firings. Low fire glaze is typically fired between 1828°F – 1945°F, medium fired glaze from 2124°F – 2232°F and high fire glaze from 2280°F – 2345°F. Your glaze ingredients and the temperature of your kiln are important partners as they work together. Your glaze surfaces can be glossy, matte or satin. Choosing the right surface for what the piece will be used for will ensure the glaze works well and protects the pottery and the user.
To add depth and difference to your artwork you can create with underglazes added to your raw or bisque fired piece. They come in a variety of colors and are available commercially, although you can make your own too. Underglazes can be used in all temperatures of firing. The final glaze firing with a clear glaze added on top to preserve it you can ensure it will remain beautiful and can be used for food for a long time to come.
Choosing the right glaze for your pottery
Choosing the correct glaze for your work can be both daunting and exciting! For tableware, functionally, your glaze recipe should fit your clay body properly with no shivering, crazing or cracking. Aesthetically, you are aiming for an easy to clean surface and a pleasing color. You can mix your own glazes from a variety of chemicals, clays, colorants and other ingredients or you may choose to use prepared commercial glazes. Your choice will dependant on factors like the space, equipment and knowledge you have.
An easier method when mixing your own glaze is to find a base glaze recipe that works for you and experiment adding different stains and oxides to develop a colorful line of glazes. Glaze can be applied to pottery using several methods including dipping, painting and spraying. Glazes are formulated for different levels of firing temperatures including lower temperature glazes.
How glaze application affects the final result
Applying the glaze is an important step in the process. If you don’t have consistency your glaze can look different every time. If you want uniform results each time you can follow a few guidelines. Firstly, it is important for consist results to know the specific gravity of your glaze once its meeting your expectations. Specific gravity is the measure of the viscosity (thickness) of your glaze. This can be determined by using a commercial or homemade hydrometer. Measure each time before you start glazing and adjust as needed. This will ensure you do not have too much glaze or too little. When dipping glaze, its good practice to do it the same every time, for example count how long you have the piece submerged. When brushing glaze, you can apply the same number of coats each time starting with your base coat to remain consistent. Keep in mind that how your glaze is used is an important step in achieving great glaze results.
To accomplish the same results over and over, test tiles are a great way to document your glazes and to test how your glaze works. You can test techniques like double dipping your coat of glaze or how an application of stain or underglaze works with your glaze. Once you have a result that you are pleased with, the test tiles remain a guide for your future use.
Understanding glaze firing and color shifts
High-temperature glazes, with a firing temperature of 2280°F and above, are celebrated for their durability and rich finishes. These typically come from gas, wood or electric kilns. Depending on the kiln, the type of fuel and where the kiln shelf is placed within in the kiln you can expect varied results. Glaze firing at this high temperature make them ideal for functional ware like dinner plates and mugs and allow for the complete maturation of glaze materials, resulting in a long-lasting finish.
Conversely, low-temperature glazes, fired from1828°F – 1945°F, are known for their bright, vivid, depth of color and energy-efficient firing process. These glazes can be accessible for beginners and their first pottery due to their forgiving nature and lower firing requirements.
Various ingredients in your glaze can help change colors including zinc. It can react with other compounds in the glaze causing hue and texture changes. Adding different percentages of stains and oxides will allow for color shifts and experimentation to find that brilliant color you’ve been searching for.
Common glazing mistakes and how to fix them
Glazing inconsistencies can happen for many different reasons. One of the more common is that the glaze recipe doesn’t ‘fit’ your clay body. If the glaze shrinks more than the clay during the firing your glaze can craze or it can cause dunting, cracking your piece entirely. Pinholes can be due to glaze application or dust on your piece before glazing. Wiping your bisqueware down with a damp, clean sponge will clean any dust off and ensure a better glaze application. Glaze consistency is very important too. When you find a consistency that works for you, measure the specific gravity using a hydrometer as discussed above. This will ensure you achieve the desired results from firing to firing. This can also prevent too much glaze and your glaze running onto your kiln shelf. TIP: If you are testing new glazes it’s a good idea to protect your kiln shelf with kiln wash and a scrap piece of kiln shelf underneath the glazed piece to catch any glaze running off during the firing .
Keep in mind that if you use different clay or different techniques this will affect how your glaze performs. Staying consistent and taking many notes in your first stages will ensure reliability into the future.
