Figure 1 Glaze The ceramic surface is rich with possibility. This is a short introduction to the vast array of surface techniques used in the ceramic arts. Glazing is the most common surface solution used in ceramics. The surface can begin to develop while the clay is leather hard. This is the perfect time to make impressions in the clay. The surface can develop with the use of slips, sgraffito and additive techniques. Glaze is basically a glassy, impervious coating that is fused to the surface of the clay by heat (Spleight & Toki, 1999, p. 332). Glazing is the process of applying materials to the surface of the clay, which will fuse and melt after being fired. Glaze can be a confusing material since the color of the glaze may change when it is fired. The finished surface may also vary depending on the type of clay body used. I recommend having test tiles available for students while they are glazing. This will help them to better visualize the final results. Show the students how to make test tiles so that they have the ability to test glazes before firing their final projects (Figure 2). Figure 2 Glaze: test tiles
There are different types of glazes, the most common are gloss, matt, and satin matt. Suppliers offer glazes with different opacities and surface textures. Gloss glazes offer a smooth shinny surface that is food safe. Matt glazes have a dull, non-glossy surface and should not be used on as food surface. Satin matt fits in between gloss and matt, and depending on the composition, it can be food safe. Make sure to ask your supplier if the glaze is safe for food. In the classroom, glazing should be done on bisque ware. If the clay has been bisque fired, it will be stronger during the glazing process. Historically this has not always been the case, but in today s classroom it is better to be safe. The type of clay body used will determine the glaze firing temperature. Make sure that the clay body and the glaze temperature match. If they do not match and the glaze temperature was lower then the clay body temperature the glaze could run off the piece onto the shelf below. You should be able to find the temperature of the clay body on the box, and the glaze temperature should be labeled on the container. If it is not listed, you should contact your ceramic supplier. Figure 3 Glaze: rinsing Before glazing, I recommend going over the piece with sand paper. It is important to keep bisque ware as clean as possible. If it collects dust or oil from your fingers the glaze might not attach properly. Be sure to rinse and dry the piece before applying glaze (Figure 3). Figure 4 Glaze: mixing
How to glaze? There are a few different techniques that can be used in basic glazing: brushing, dipping, pouring, and spraying. If you buy your glaze premixed from the ceramic supplier, it will come in a pint size (Figure 1). Pint size containers are convenient to store and move throughout the classroom, but the small quantity will limit the types of application that can be used. Brushing The brushing technique is painting with glaze (Figure 5). When brushing on glaze, you should only need 1-3 coats depending on the thickness of the glaze. Over time the glaze mixture will dry out, so it is best to check the viscosity before application and add water if need (Figure 4). The downfall to brushing is that it can leave streaks on the surface because bisque ware is porous and absorbs the glaze quickly. When done purposefully the brush will leave a beautiful mark. Special brushes are not needed for glazing, but it is smart to keep your glaze brushes separate from your painting brushes used for watercolors, acrylics, oils, etc. You should provide students with a variety of brush sizes that offer different types of application. For example, student may use larger, flat brushes to cover large surface areas and a smaller, pointed brush for fine details. Figure 5 Glaze: brushing Dipping Dipping is done by submerging a piece in glaze. This is the easiest form of glazing, but it requires a large amount of glaze. Dipping will create an even coat of glaze on the surface. While the amount of time varies depending on the thickness of the glaze, submerging a piece for a few seconds will typically produce good results. You can use your hands, but tongs are recommended. The small marks left behind by the tongs can be easily fixed with a dab glaze using your finger or a brush. Figure 6 Glaze: dipping
Pouring Pouring is to pour the glaze over the surface of the piece (Figure 7). It is the best way to glaze inside a narrow necked piece and is used to create surface designs when poured over the outside. When pouring glaze, you should have two containers: one that holds the glaze and another to catch the run off glaze. The advantage to this technique is that you will not need large amounts of glaze. The glaze that runs off can be reused and put back into the original container or poured again. When pouring, the glaze coat will be somewhat uneven, and tends to run. It is common for pouring and dipping techniques to be used together. Figure 7 Glaze: pouring Spraying Spraying glaze can be hazardous to your health. If you plan to use this technique, make sure you have a spray booth with proper ventilation and that you always wear a mask. A N95 dust mask will be sufficient. Glaze is sprayed with a spray gun that is hooked up to an air compressor (Figure 8). It takes time to learn how to spray glaze. When this technique is mastered, it can be used to create a variety of surfaces, including interesting effects with layered glazes. When attempting to build up the surface with glaze, it is helpful to put food coloring in the second coat of glaze to help guide you as the glaze is applied. The food coloring will not affect the final glaze color because it will burn away in the kiln. The advantage to spraying is that you do not need a large amount of glaze. Also using the spraying technique allows you to have control over how much glaze is applied to the surface.
Figure 8 Glaze: spraying After glazing, be sure to sponge the glaze off the bottom of the piece or make sure to place the work on stilts while firing to prevent it from sticking to the kiln shelf. I tell students to leave at least ¼ of an inch at the bottom with out glaze if they are not going to stilt the pieces in the kiln. If you need more information on glazing, check out the resources provided below.
Bibliography & recommended readings Daly, G. (1995). Glazes and glazing techniques: A glaze journey. Orlando, FL: Gentle Breeze Publishing. (p. 90-130) Hopper, R. (1984). The ceramic spectrum: A simplified approach to glaze and color development. Radnor, PA: Chilton Book Company. (p. 3-20) Peterson, S. (2000). The craft and art of clay. Upper Saddle River, NJ: Prentice- Hall Inc. (p. 101-125) Reason, E. (2010). Ceramics for beginners: Wheel throwing. New York, NY: Lark Books, A division of Sterling Publishing Co, Inc. (p. 113-118)