Glazing is a crucial step in pottery, serving both functional and aesthetic purposes. It transforms a porous, bisqued piece into a durable, waterproof vessel while simultaneously offering a canvas for artistic expression through color and texture. Without a glaze, earthenware, for example, remains porous and unsuitable for holding liquids, highlighting the necessity of this process. Glazes not only enhance the visual appeal of pottery but also ensure its longevity and utility.
There are many different types of pottery glazes available, and all provide different results, depending on your preferred finish and end-use. Ash glaze is made from plants or wood ash. Glazy categorizes clay bodies by type and then usage, for instance: Porcelain – Slipcasting. Glazy originally adopted the format of John Britt’s The Complete Guide to High-Fire Glazes, Glazing & Firing at Cone 10. It is a glaze used to coat the product and then act as a transparent glass that is applied to the surface of the product to be transparent until the color of the clay or the color decorated on the surface of the clay can be clearly seen. Opaque Glazes is a glaze that can completely cover the surface of the clay. High Fire Glazes are glazes fired at a temperature of approximately 1,230 – 1,460 °C, with feldspar and limestone as the main raw materials to help melt the glaze together with silica and kaolin. Low Fire Glazes are glazes that are fired below 1,100 °C. Glaze is also used on stoneware and porcelain. An understanding of the different types of ceramic glaze available is a great starting point. You may even want to learn how to make your own glaze for pottery. Also, you may want to know more about luster glazes.
Types of Glazes and Their Properties
The world of pottery glazes is vast and varied, offering an array of options to suit different aesthetic preferences and functional requirements. Glazes are often categorized by their firing temperature, such as low fire (cone 06-04), mid fire (cone 4-6), and high fire (cone 8-10). Low fire glazes are known for producing strong colors without requiring as much energy to fire, while mid fire glazes strike a balance between vivid colors and durability, making them suitable for functional ware. High fire glazes, though fewer in commercially produced options, are known for their robustness and are often used in gas kilns.
Beyond firing temperatures, glazes can be further classified by their appearance and composition. Clear glazes, for instance, are transparent and highlight the underlying clay or decorations, while opaque glazes completely cover the clay surface. Specialty glazes like raku glazes enhance colors to create a bright and vibrant finish, creating metallic and iridescent effects. Textured glazes, on the other hand, can give pottery a pitted, cobbled, mottled, or frothy look, adding a tactile dimension to the finished piece. Bristol glazes use zinc oxide as a key melting aid in place of calcium oxide.
This video from Pottery to the People shows a great way to add rainbow speckles to your glaze. It’s a fun and easy technique to try!
Ultimately, the choice of glaze depends on the desired effect, the type of clay used, and the firing capabilities available. Experimentation is key to discovering the unique possibilities that each glaze offers, allowing potters to create pieces that are both functional and aesthetically pleasing.
Tools, Equipment, and Glazing Techniques
Before diving into the glazing process, it’s essential to gather the necessary tools and equipment. These tools aid in the preparation and application of glazes, ensuring a smooth and even finish. Brushes, available in various shapes and sizes, are fundamental for applying glaze to specific areas or creating intricate designs. Dipping tongs provide a safe and efficient way to immerse pottery pieces in glaze, while spray guns and atomizers are useful for applying glaze in fine mists or layers, particularly in studios with proper ventilation.
In addition to application tools, mixing utensils such as spatulas, whisks, and the Jiffy Mixer are essential for achieving a consistent glaze mixture. Sieves, available in different mesh sizes, help remove large particles that may disrupt the glaze’s composition, ensuring a smooth application. Measuring cups and scoops are necessary for accurate glaze preparation, while hydrometers help determine the density of the glaze by measuring specific gravity. For personal protection, potters aprons and HEPA vacuums for clay studios are vital
Once the tools are assembled, the glazing process begins with preparing the bisque-fired piece. This involves ensuring the pottery is free of dust, oils, or any other contaminants that may interfere with glaze adhesion. The glaze is then mixed to the correct consistency, typically resembling thick paint. Applying the glaze can be done through various techniques, including dipping, pouring, brushing, spraying, splattering, stippling, sponging, glaze trailing, and glazing with wax resist. Dipping provides a smooth, even coating, while brushing allows for more precise application and decorative effects. Each technique offers unique advantages, and potters often combine multiple methods to achieve their desired results.
Glazing Challenges, Firing, and Safety
Despite careful preparation, glazing can present several challenges. Common problems include crazing, where fine cracks appear on the glaze surface; pinholing, characterized by small holes in the glaze; and crawling, where the glaze pulls away from the clay, leaving bare patches. Crazing is the most common glaze defect, and normally the easiest to correct. In both crazing and shivering the eradication of problems relies on matching the thermal expansion characteristics of both body and glaze. Shivering is the most problematic of glaze defects, particularly in any functional ware, since slivers of glaze from the edges can drop into food or drink. Crawling is caused by a high index of surface tension in the melting glaze. Pinholes can occur in underfired or viscous glazes, where gases have escaped during firing but have not healed over.
Troubleshooting these issues often involves adjusting the glaze composition, firing schedule, or application technique. For instance, crazing can be corrected by increasing the silica content in the glaze, while pinholing may require a longer firing cycle or a more fluid glaze. Addressing crawling may involve calcining materials with high drying shrinkage such as china clay and zinc oxide and reducing materials with high surface tension such as zirconium and tin oxide.
Once the glazing is complete and any necessary adjustments have been made, the pottery is ready for its final firing in the kiln. Proper loading techniques are crucial to ensure even heat distribution and prevent pieces from sticking together. The firing schedule, which dictates the rate of temperature increase and the final temperature, must be carefully followed to achieve the desired glaze results. After firing, the pottery undergoes a final inspection to assess the glaze’s appearance and functionality.
Safety is paramount throughout the entire glazing process. Many glaze materials are hazardous and inhalation of all clay materials especially silica can damage your lungs. It is also essential to use a Ceramic dust filter mask that fits well when mixing, spraying, or sanding glazes. Lead, cadmium, and lustre glazes are particularly volatile at low-medium firing ranges. Copper, chrome, and tin glazes are volatile in high-firing ranges.
By following these guidelines and prioritizing safety, potters can master the art of glazing and create beautiful, functional pieces that will be treasured for years to come.
