In preparation for glaze firing, most clay artists bisque fire their work. The goal of bisque firing is to heat the work so that the clay is partially vitrified but still porous enough to accept glaze. At Odyssey, our best practices include bisque firing all our work to cone 04, though you will definitely find some variation among artists. Though a small amount of energy costs may be saved in firing to a lower cone, we have found that bisque firing to cone 04 gives the organic material in the clay more time to burn off, thus reducing problems such as pinholing in the subsequent glaze firing(s).

Be consistent in whichever cone you use to bisque, as the porosity of the bisque will dictate the degree of absorption when you glaze your work. This becomes important particularly if you use the count system as described shown here. Bisque fired at a lower temperature will absorb more glaze in the same period of time as bisque fired to a higher temperature.

Bisque firing can be done in either an electric or gas kiln. If a gas kiln is used, an oxidizing atmosphere should be maintained throughout the firing by keeping the damper wide open to allow plenty of oxygen to circulate in the kiln. Make sure your work is bone dry before bisque firing.

Though it is possible to force-dry work using a preheat, please note that this does use fossil fuels to dry the work when time could have done the same thing. Additionally, it should be mentioned that preheating the kiln requires that the relays and elements in your electric kiln turn on and off several hundred more times than in a normal firing. This additional wear and tear will cause them to be replaced earlier, and these repairs are not cheap! However, preheating can be necessary for large or thick work, and super helpful when you are under a deadline.

Some people choose to tumble stack their firing, resting pots lip to lip or foot to foot. Others nest work, placing smaller pieces inside of larger ones. Both of these methods save space in the kiln, but can have some drawbacks, including reduced airflow in certain areas that can create pockets of reduction, such that the bisque may be visibly discolored. This can affect the results of later glaze firings. To avoid this problem, place work in the kiln with ¼ inch (6 mm) in between pieces, and at least ½ inch (1 cm) away from the elements. Try to clear the first two sets of elements before putting a second shelf in (5-inch [13 cm] stilts should do). Otherwise, it is difficult to bring the bottom shelf to temperature. Also try to leave a 2 inch (5 cm) clearance from the lid.

We use vent systems with our electric kilns. Air is introduced from the top and pulled through the kiln using a motorized draw fan. The extra 2 inches (5 cm) of space we leave at the top makes sure that the ware does not end up in a cool spot created by the draft holes or from a lid that does not sit flush. To function correctly, vented kilns require that all of the spyhole plugs be inserted, but they offer more even firings and a smooth cooling. You can fire your kiln unvented, but it should be in a well-ventilated area to avoid building up any harmful gases released during the firing.

I recommend placing silica sand or grog underneath larger pieces so they can move as they shrink in order to reduce cracking around the foot of the piece. These materials can be reused repeatedly. Just vacuum out the kiln between firings.

If your electric kiln is computerized, use a “slow” fire program to bisque rather than a “medium” or “fast” program. Make no exceptions unless you are willing to risk a kiln full of shards. This program works well for pieces that are ⅜ inch (9 mm) thick or less.

Standard (Slow) Bisque Fire Profile

This firing schedule will take approximately 12 hours and is recommended for the majority of bisque fired ceramic work. For large, thick (⅜ inch [9 mm] thick or more), or sculptural work, we use a slightly different program, which follows.

Large/Thick Bisque Fire Profile

This program does rely on a long preheat held at 180°F (82°C). When weighed against the amount of energy it would take to remake and fire the work if it cracked in the bisque, the preheat is worth it for specialty pieces.

When your kiln has cooled to below 250°F (121°C), you can open the door. I usually wait until the temperature is 150°F (66°C) or below to unload, and at that temperature you still may need gloves. I then vacuum the kiln and use compressed air to blow any dust off of the surface of the work. At that point the bisque is glazed and allowed to dry, ideally overnight.

I always feel a sense of satisfaction at this point, knowing the care and attention that has gone into the making and glazing of the work, but also excitement in anticipation of the finished products. I expect good results, but that being said, I frequently experience a twinge of anxiety because each firing is unique. The mass of the pots inside the kiln, the wear and tear on the elements, the degradation of the thermocouple—all can affect the firing in noticeable ways. So we pack the kiln carefully, set our cones, and say goodbye to our glazed bisque, set to emerge from its cocoon of fire several days later, metamorphosed.

In loading the glaze kiln, all of the same best practices apply to glaze firing as to bisque firing. There are several more important considerations in addition. Make sure that all glaze is cleaned off the bottom of the pot, and perhaps ⅛ to ¼ inch (3 to 6 mm) up the side. Some people wax the bottom of the pieces before glazing. Others choose to wipe it off with a sponge or to use a wet piece of carpet (opposite).

Wadding and Cookies Wadding is a type of clay made from extremely refractory materials (usually 50% EPK and 50% Alumina Hydrate). I use wadding to lift pots off the shelf. This is absolutely necessary for salt and wood firing so that the atmospheric glaze doesn’t fuse the pots to the kiln shelves, but it can also be used underneath pots in any kiln when glazes have a tendency to run. Keep your wadding in a tightly sealed container, as it does have a tendency to dry out quickly.

Cookies are flat pieces of stoneware clay that have been kiln washed on one side or simply left as they are. If you are using runny glaze combinations, we highly recommend placing your piece on top of several balls of wadding that have been glued to a cookie (see photo opposite). Though this process takes some extra time during loading, it saves many headaches (and remaking many pots!).

It is unlikely that you will find yourself standing in front of a gas kiln with only this book to explain how to get a great reduction firing. More likely, someone who has more experience with the kiln will teach you the ins and outs of firing it: how to avoid stalling out at high temperatures, where the pockets of good reduction are, and just how far you need to push the damper in to get the kiln to reduce adequately. This oral transmission of knowledge from kiln master to kiln neophyte is an incredibly important part of learning how to fire. If you are able, ride along with this person for several firings, and then have them shadow you until you really get the hang of it.

Here are some general guidelines to get you ready: Though oxidation firings can be done in an electric or a gas kiln, reduction firings (which “reduce” the available amount of oxygen in the kiln to influence the color and texture of glazes) are generally the provenance of gas-fired kilns.

For reduction firing in a gas kiln, you will need to monitor both the rate of climb and the atmosphere inside the kiln. The amount of oxygen present in the kiln can be manipulated by moving the damper in or out. Very small movements of the damper, as little as ⅛ inch (3 mm), can cause noticeable differences in the amount of reduction.

At Odyssey we fire a twenty-four-year-old Geil kiln, beginning in oxidation with the damper open 2½ inches (6 cm) until the kiln reaches cone 012 (1582°F/861°C). When cone 012 begins to bend, we push the damper in to deprive the kiln of oxygen by reducing airflow. The temperature generally falls with heavy reduction as some of the gas will not completely combust, which creates carbon monoxide that in turn reduces BTUs. We begin by reducing heavily for about five minutes and then start pulling the damper out until we achieve a “climbing reduction” where the temperature inside the kiln goes up approximately 60°F to 80°F (16°C to 27°C) per hour, or approximately 1 degree per minute. We continue firing this way until the kiln reaches cone 04 (1946°F/1063°C). This generally takes four hours or so. When cone 04 bends, we open the damper back up and continue to fire the kiln until it reaches top temperature.

Reduction Glaze Fire Profile

Turn the gas off and push the damper the whole way in to allow for a slow cooling. Whether you are oxidation glaze firing in an electric kiln or reducing in a gas kiln, the ware should be allowed to cool slowly. Only open the kiln once it’s back to room temperature. If you have to peek—and do try to resist the impulse—make sure the kiln is 250°F (121°C) or below, and do not open the kiln door until the temperature is 150°F (66°C) or below.

The fastest and most immediately gratifying of glaze techniques, raku is a lightning-quick firing, but it requires attention and a practiced choreography. Most raku kilns are portable and fired with propane, but you can create a hard-plumbed version with natural gas. The materials are relatively inexpensive, and there are numerous designs available online. A simple raku kiln can be made for less than $200 (€165).

Both sources of fuel work quite well and follow the same basic set of steps: First make sure that you have set up all of the appropriate safety precautions. You’ll want to place a fire extinguisher and a 5-gallon (19 L) bucket of water within reach. Tie long hair back. Don’t wear loose clothing. Do wear closed-toe shoes. (For a kick, check out adorable maniac and raku legend Paul Soldner’s innovative take on “naked raku.” The Paul Soldner Appreciation Society meets at Odyssey once a month.)

When you have set the stage for a safe firing, load the kiln, leaving at least ¼ inch (6 mm) between pieces as the glazes will bubble up during the firing. Then using 3 to 5 pounds of pressure, light the burner and close the chamber of the kiln. You can fire a raku kiln in a remarkably short period of time. If you have a pyrometer, the rate of climb can be as high as 2500°F (1371°C) per hour. If you do not have a pyrometer, you can still gauge the firing by using the spyhole and paying close attention to the glaze on the surface of the ware. You will notice that as the kiln goes from red to orange heat, the glaze on the pots will swell, bubble, and then flux out into a liquid and appear quite glossy. The whole process may only take 30 to 45 minutes.

While the kiln is heating up, fold standard newspaper into long strips. Soak them in water, and line the rims of the buckets with the wet newspaper. This will act as a grommet for the lid on the can and ensure a good seal. Fill the cans halfway with combustibles such as newspaper or sawdust. Note that some glazes, such as Raku Love, require as little as a single piece of newsprint in the can to create the light blue effect, while heavier reduction can give quite a different look (see tile shown here).

You will want to confirm that all of the pieces have fully bubbled and become fluid again before cutting the gas to the kiln and opening it up. Carefully remove the works with tongs and place them in the galvanized steel buckets filled with the combustible materials. The combustibles will ignite immediately. Let the fire catch and burn for fifteen to twenty seconds and then place the lid on the can. The can should begin to smoke heavily. Some people open the lid of the bucket after a minute or two to reignite the flame. Be careful and back away from the kiln when you pull the lid! The flame can jump several feet (1 m) out of the can when it reignites. After ten seconds, the lid should again be placed down tightly on the bucket with the ware then allowed to reduce and cool for 30 to 45 minutes. The pieces are then dipped in water to “freeze” the colors and then cleaned with steel wool to remove any excess carbon.

I classify pots fresh from the kiln in several categories:

Firsts These are strong, unflawed pieces that meet my standards of aesthetic appeal and functional strength. I am proud to present this work as my own.

NOTE There is a small subcategory of firsts that I call “Pots that Sing.” These have been “kiln kissed” and occur perhaps one in a thousand pieces. These should be kept or given as gifts to people you love. In some cases, money can actually detract from a piece that feels priceless!

Seconds These may have the occasional pinhole or the glaze may be a little too thick or too thin. Sometimes they warp a bit in the kiln. They may lack the luster I desire for a gallery or museum, but I don’t mind putting them on the sales table when I do the local farmers’ market.

Thirds These ruffians do not get to see the light of day. I will not sell them in any official capacity, but I do have a small collection of the ugliest pots I have ever made; they serve to remind me to approach things in a lighthearted way.

ALTERNATIVE DECORATING MATERIALS

Like a canvas, bisque fired clay receives Cray- Pas, colored pencils, acrylics, markers, and spray paints quite well. You can draw or paint directly on the surface of the fired clay. If you tried to fire any of the products to ceramic temperatures, you would find they would almost entirely burn out.

To seal the work and provide a protective layer of gloss, there are several commercial products, including Duncan Ceramic Spray Sealers, that give a hard, clear finish on top of fired bisque. Application is easy. Just hold the spray can 6 to 8 inches (15 to 20 cm) away from the surface and spray three coats, letting them dry in between. Wear a dust mask or respirator and spray these products in a well-ventilated area. Floor wax or polyurethane can also be used as an inexpensive sealant, and gloss coat and may be applied with a brush. Like the spray enamels, you may need to apply several coats to get the degree of gloss you are after.

Isabelle Coppinger and the Decision Not to Glaze

Although Isabelle Coppinger uses a number of fired glaze techniques in her work—including low-fire clear glaze, gold luster, and her namesake Isa’s Bomb Blue (here)—it is her unglazed, white earthenware wall installations that have found an international audience. Featured in private homes, galleries, and hotels, patrons regularly commission her to create custom designs that bring life, energy, and a sense of movement to their space.

Isa’s process starts by rolling out a cart full of ¼ inch (6 mm) slabs of white earthenware, each approximately 2 by 3 feet (60 by 91 cm). After letting them air-dry and stiffen sufficiently, she attacks them with the graceful precision of a martial artist, executing a series of X-ACTO knife cuts that create a standardized form reminiscent of a butterfly’s wing. Other supporting pieces for the installation are created out of several hundred slivers cut from the slab, carefully curved and placed together to create geometric, patterned flora. The individual pieces are fired to cone 02. Any rough areas are sanded when they are removed from the kiln. Depending on the effect Isa wants to create with the installation, some pieces are spray-painted with enamel while others are left natural and untreated.

>The individual pieces recombine in patterns that have been carefully orchestrated in advance. Isa’s artistic vision is clear, and her attention to detail ensures that it is cleanly executed. For this reason, Isa requires (through binding contract) that the patron allow her to install the work, which she includes in the purchase price. Isabelle installs each piece herself, sometimes aided by her sister or friends. The act of the install is an integral part of her artistic process and takes place over several stages. First, in the studio, mounting rods are carefully attached to the pieces using two-part epoxy and then allowed to cure. The pieces are then wrapped for transport and driven to the installation site in the most unlikely of cargo vans—Isa’s iconic, antique white Mercedes 300D Turbo Diesel. The decision not to glaze the work becomes obvious when the work is installed. Light plays differently off raw fired clay than it does glaze, and the earthenware seems to glow with its own energy.

In her spare time, you can find Isa working on restoring the Turbo. I once watched a man approach her while she was working on the car outside of her apartment building. He asked if she needed help, and I’ll never forget the dejected look of disappointment on his face when she nonchalantly told him, “Nah, I got it.” Indeed, she does.

Post firing, you may want to make some textural changes to your work. Sometimes glaze will run off the side of your piece creating a super sharp edge. Other times you will end up with a bit of kiln wash or sand on the bottom of your piece. Whether you need to smooth it out or rough it up, here is a primer on the best and safest ways to alter the texture of your work.

DIAMOND GRINDING

In nature, time and pressure create diamonds over millions of years, but humans have figured out how to accelerate the process in labs, and this is of great benefit to the clay artist. Pricey, but worth every penny ten times over, diamond grinding bats, Dremel attachments, and sanding sponges come in a variety of grits, from 60 to 3000, and are categorically the best way to remove unwanted glaze, smooth out rough areas, and help a rocking piece to sit flush.

Several companies, including DiamondCore and His Glassworks in Asheville, North Carolina, produce diamonds bats that come with adhesive on the nonabrasive side. These can be attached to a standard wooden bat, thus turning your potter’s wheel into an instant grinding station.

The grinding process is rather loud, so you may want to move your wheel outdoors or away from studio mates. You’ll want eye protection and a dust mask or respirator, even if you are grinding wet, which we recommend. Diamond grinding bats are the quickest way to remove unwanted glaze from the bottom of a piece, and much better suited to cleaning pottery than a bench grinder. A diamond grinding bat can also help level a pot that rocks, an annoying but common defect. When using a diamond grinding bat, grip the piece tightly with both hands and make sure not to scrape your knuckles against the spinning disk.

Once the glaze has been removed and the piece leveled, detail work to finish the piece can be carried out using a diamond Dremel attachment. Diamond sanding sponges should be used to buff the clay to a buttery smoothness. I have always been impressed by the feel of Sara Ballek’s work. Once removed from the glaze kiln, Sara uses a series of diamond sanding sponges on her work (from 60-grit all the way to 3000) to create a clay surface so smooth it feels like marble.

NOTE Many people overlook this important last step, but pay attention to the bottom of your pieces so that there is no way they can scratch the beautiful mahogany table where they may end up. Created, dried, bisque fired, glazed, and sanded to a sheen, your work is now ready to present. I encourage you to take pride in the accomplishment. There is joy in creating something beautiful from top to bottom.

Dr. Paul Silverman’s Trompe l’œil Sculptures

A favorite personality at the Clay Works studio, Dr. Paul Silverman is a skilled researcher who organizes international conferences on the study of cancer. Author of several books on the subject, he has dedicated a career to working on one of humanity’s most pressing medical issues. When we see him in the clay studio, however, it is a joy to watch Dr. Paul’s inquisitive mind pursue answers to technical questions regarding the execution of his excellent trompe l’oeil sculptures.

Dr. Paul originally started making clay replicas of antiques from the toolshed in the house where he grew up. Using these artifacts as sources, an incredible array of sculptures emanated from Dr. Paul’s skilled hands. We soon featured him in our gallery and the response was tremendous. Visitors simply could not believe that these works were made of clay and not metal. People began bringing him examples of old tools they loved, and we’ve witnessed some really poignant moments of nostalgia and human connection on the gallery floor.

Dr. Paul has since moved on to the subject of classic kitchen tools. He recently created a raku fired nutcracker, a rocking parsley knife, and classic cheese grater. His process is a combination of slab work and free sculpting, using a heavily grogged clay body. Each piece presents a unique challenge, so he often works from models or photographs. It has been a pleasure to watch him grow as an artist through this series of truly ambitious sculptures.

Dr. Paul uses several products to create various effects, including commercial glazes and underglazes, as well as custom recipes he developed to imitate rust and weathering. To develop a glaze that looks like rust, Dr. Paul did a series of triaxial blends using crocus martin, red iron oxide, and rutile. After several sets of tests, he landed on a combination that truly fools the eye. Although the work only spent a night in the kiln, it looks like it was made in the last century. In order to further “age” his work, Dr. Paul will sidle up to the sandblaster and take down a couple layers of the surface. The sandblaster is an efficient way to give pieces a weathered look. The finished product feels as if it had hung in a barn for decades. Dr. Paul’s work reminds us that clay is one of nature’s greatest mimics, that a skilled hand can still fool the eye, and that good artwork gives us the opportunity to make meaningful human connections.

*The column for “small cones” covers both juniors and bars.