Pottery glazes are complex mixtures that fuse to pottery when placed in a high temperature kiln. Glazes are responsible both for decorating the pottery and for creating an attractive glossy surface that protects the pottery from wear and water. While glazing can be a long and involved process, it is not too hard to learn, and results will improve with practice. If you don’t have access to a kiln, try to find one before you begin, as described within the Firing section below.
Choosing Pottery and Glazes
Start with an unglazed, hard ceramic. A ceramic shop or artist might direct you to suitable objects they sell. Typically, these objects have gone through a “bisque” firing process to make it hard. Unlike some types of fired ceramic, bisque has a porous, absorbent surface. This allows it to absorb wet glaze, which will then create a protective waterproof finish when the ceramic is fired a second time.
Depending on the type of clay used, the bisque ceramic may be white or red.
If you have a clay object you made yourself, fire it in the kiln to make it hard but still porous before you glaze. The exact temperature to fire your object depends on its size and type of clay, so if possible ask the advice of an experienced potter. One may be willing to let you use his or her kiln, although the potter may ask for compensation.
Wear disposable gloves while handling the ceramic. The plain “bisque” object you will be glazing should be kept as clean as possible. Even oil from your hands may prevent the glaze from attaching correctly, so wear disposable latex gloves whenever you touch the object you will be glazing. Change them whenever they get dirty, before touching the ceramic.
Purchase pre-mixed glazes if possible. While you may mix your own glazes out of dry powder and water, doing so requires a respirator mask to avoid inhaling what is essentially particles of glass dust. Pre-mixed glazes are less likely to cause problems during firing as well, especially if you have never mixed your own glazes before.
Consider glazes based on their firing temperature. Different glazes require firing at different temperatures to set correctly onto the object. Do not use two glazes that require different firing temperatures on the same object, or you will risk breaking the pottery.
Firing temperatures may be listed simply as “high” or “low”, or referred to as “cone 2”, “cone 4”, et cetera. These measurements refer to potters’ cones made from different clay types, which sag at different temperatures in the kiln.
Be aware of harmful glaze ingredients. Ask what the glaze is made from before purchasing. Lead-based over-glaze are not recommended for objects that will come into contact with food or drink. Toxic glazes of any type are not recommended if children are involved in the glazing process or have access to the area you will be storing the glazes.
Lead-based underglazes with a protective non-lead overglaze will probably be safe initially, if the glaze was fired properly. However, lead may begin to leach through the glaze after prolonged use, especially if the ceramic is frequently scrubbed or exposed to high-acid foods such as tomatoes. Stop using the dish immediately if you see powder or cracking at the glaze’s surface.
Purchase one or more underglazes based on their post-firing color. Underglazes come in a variety of colors and are intended for decorating or painting an object. You may use as many colors of underglazes as you like to decorate your pot. However, realize that glazes undergo a chemical process inside the kiln that can alter their color dramatically. Look at the colors on the manufacturer’s glazing chart to see examples of the glazes’ final color. Do not assume a fired glaze will look the same as it appears before firing.
Purchase an overglaze. Whether or not you decide to decorate your ceramic object with underglazes, you will always require a single overglaze. This creates a glossy, protective finish over the surface of the object. Pick a clear overglaze that won’t hide the color of the underglaze(s), or if you aren’t using underglazes, pick an overglaze of any color.
Note: As described above, you must use glazes that fire at the same temperature if you are using multiple glazes on one object. If you fire a glaze at the wrong temperature, your object could be damaged.
Preparing the Object and Glazes
Sand bumps or imperfections off the surface. If you notice any bumps on the object that aren’t supposed to be there, you may sand them off using 100 grit sandpaper until you create a smooth surface. Be sure to wipe the object afterward with a damp sponge to remove dust created during sanding. If you purchased an object intended for glazing, most if not all imperfections should be removed.
Wipe the ceramic with a damp sponge before you begin and whenever it gets dirty. Before you begin, and whenever the ceramic becomes dirty or you apply too much glaze, wipe with a damp sponge. Avoid rinsing or dripping excess water onto the ceramic. Use each side of the sponge sparingly to keep it as clean as possible; you may want to have several on hand.
Remember, you should reduce the amount of dirt or oil on the ceramic by wearing disposable gloves whenever you handle it.
Apply wax to the base of your object, and wherever two removable parts meet. A coating of wax prevents glaze from sticking to the base of the ceramic, where it would “glue” your object to the base of the kiln. For the same reason, apply the wax to the rim where a lid touches, or anywhere else two distinct pieces will touch during firing. While some potters use slightly heated paraffin wax for this purpose, a safer and less smelly option is “wax resist” designed for this purpose at ceramic shops or some art supply stores. You may apply wax resist and apply it with a paint brush. Keep this brush separate from your glazes.
Crayons may be rubbed on the object to create a wax coating, but there is a possibility that the colors in the crayon wax end up on your pottery.
If you are glazing pottery with children, you may find it easier to skip this step and hot glue the children’s glazed objects to a clay disc immediately before firing, in order to catch dripping glaze.
If you are mixing your own glazes, follow instructions and safety procedures carefully. A pre-mixed glaze is recommended for your first few projects (at least) due to the safety hazard and difficulties involved in mixing your own glaze. If you do decide to mix a dry glaze powder with water, follow the manufacturer’s instructions carefully or your glaze may not achieve the desired characteristics. Always wear a respirator mask to avoid inhaling dry glaze particles, and work outside or in a well-ventilated room. Do not let anyone near the work area without a respirator mask. Gloves and safety goggles are recommended.
While full instructions are not included here due to the variations between different glaze mixes, you will need water, a long stirring spoon, and a hydrometer to test the density, or “specific gravity”, of the glaze.
Applying the Glaze
Stir each glaze thoroughly. Even if you purchased pre-mixed glazes, they may require stirring to return them to an even consistency before you apply them. Follow the instructions on the packaging and stir until there is no sludge on the bottom or watery layer on top.
Pour each glaze into a small dish with its own brush. Keep each color separate and use different brushes to avoid mixing them. Pour them into a small container rather than dipping the brush directly into the jar. This helps keep the remaining glaze clean for later projects.
Apply the under-glaze with your brushes. Decorate the object however you wish using brushes dipped in the underglazes. This is an open-ended process, and you may choose to get creative and drip, flick, or even spray the glaze on if you want a different effect than detailed brushwork. It is also completely acceptable to cover the entire surface with a single underglaze if you want a simple, solid color.
Keep in mind the final color of each glaze when you choose your design.
Intentional drips are often used to great effect by ceramic artists, but be aware that thick drips may alter the texture of the pottery and could cause improper firing.
Scrape off undesired glaze with a metal object. If you apply glaze in the wrong place, or if it begins to drip, scrape it off with a knife or other metal object. Wipe with a damp sponge afterward.
Clean the knife thoroughly in hot, soapy water before using it for food-related purposes.
Glaze the inside of hollow containers with narrow openings. If you are glazing a ceramic pot, mug, or other object with an inside surface, it may be difficult to see inside or reach in with the brush. Instead, you could pour a small amount of glaze inside and roll the object around in your gloved hands to apply it evenly.
Let each layer of glaze dry before applying the next. Before you attempt to apply a different color of underglaze, or the final overglaze finish, you must wait for your ceramic object to dry. This will happen faster if you keep it in an area with good air flow. Do not apply a new type of glaze until the old glaze no longer appears shiny and wet, and does not smudge when your brush touches it.
Finish by applying an overglaze. If you have a pair of potter’s tongs, the easiest way to accomplish this is to pick up the object with the tongs and dip it in a container holding the overglaze for one to three seconds. If you would like a thicker, glossier finish, dip the object for a shorter period of time, allow to dry fully, then dip again. You may dip several times, but the total application time of all dips should be no more than three seconds. You may also brush on the overglaze. Do this so the surface is completely covered with a thin layer. It is better to allow the ceramic to dry and apply a second thin layer than to apply too much glaze in one go.
Wipe off glaze from surfaces that will stick to the kiln. Also, wipe them from surfaces that will be in contact with other ceramic objects in the kiln, such as a lid. If you followed the instructions above, the base of your object should be coated with wax. This will make it easy to wipe off any glaze drips that would otherwise attach your object to the floor of the kiln. Use a clean, damp sponge.
Wipe off glaze from these surfaces after each application of glaze, before it dries.
If your glaze seems runny or drips heavily, you may wish to leave the bottom 1/4inch (6mm) or more of the object’s sides unglazed. Even many professional artists do this.
Firing the Glaze
Search for a publicly accessible kiln. Purchasing your own kiln can be expensive. If you live near an urban area, there are likely pottery studios that allow anyone to rent space in the kiln. Search online for kilns in your area, or for pottery studios that you could contact and offer to rent kiln space from.
If you live in the United States, this listing of kilns may be helpful, although there are many more not listed.
Seek experienced assistance if you need to purchase or operate your own kiln. If you end up needing to purchase a personal kiln, you’ll probably want a more portable electric kiln. There are many factors to consider, including expense, wiring, and which additional tools to purchase. Kiln operation is complex and potentially dangerous, and you may wish to find an experienced potter to guide you through the first few times you use it.
Fire the glaze according to instructions. Glazes are either low temperature or high temperature, and firing them at the wrong setting may cause the ceramic to break or the glaze to fail to set. Make sure the kiln you are using is set to the correct “cone” as described on the glaze packaging. If you are dropping off your ceramic object at a studio for the employees to fire later, include a note detailing the firing temperature. Do not attach this note directly to the glazed object.
Retrieve your ceramic after several hours. There are many different ways to operate a kiln, and some processes may require more time than others. Regardless, you should allow several hours for firing before your object is ready. If the kiln is used by many people, your object may not be ready for a day or two. Once it is done firing and has completely cooled, your object should be ready to take home and admire.
Note that your wax should burn off in the kiln. If it is still attached, or has melted onto the glaze, try using a different type of wax next time.
Clean your materials as frequently as possible to avoid mixing materials. Keep your wax brush and glaze brushes separate unless completely cleaned in between uses.
There are hundreds of types of pottery and glazes. An experienced potter or specialized pottery instruction book may be able to teach you many more methods of decorating ceramic or creating unique effects with the glaze.
Try not to apply too much glaze, or it will run and create an uneven coating. Use enough with each layer to fully coat the object, but no more.
Things You’ll Need
“Bisque” ceramic object
One or more underglazes (that fire at the same temperature)
Two or more brushes
Clean containers for glaze mixing
Metal object for scraping
How to Fire Raku Pottery
How to Make Pottery
How to Test a Pottery Glaze Using a Mortar and Pestle
How to Paint Lines of Pottery Glaze
How to Paint Pottery
Sources and Citations
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