Methodologies

The Making Process

Pottery starts as soft material that comes from the earth: clay.  Many of us are familiar with it from childhood - either in its raw form or as a like-kind substance such as play-doh or modeling clay.  It is where everything starts, as we form it on the potter's wheel or through various hand building techniques in its soft, hydrated, plastic form.  There are myriad clays which have unique properties that influence everything from their performance in different forming techniques, what glazes they are compatible with, their appearance and texture when fully fired, as well as their durability and strength.

After the clay is formed in its moist condition, it is allowed to dry partially to what is known as the "leather hard" state.  In this condition, the clay is still somewhat workable but holds its shape, is less easy to deform, and is able to be trimmed.  Trimming is much like working with wood on a lathe, where a bladed tool is used to remove clay from and refine the shape of the leather hard form as it spins on the wheel.  This stage is also often when potters will carve or attach handles to the form.

After the pot is trimmed and finished, it is allowed to dry completely until "bone dry."  This is when pottery is at its most fragile and much care is taken to make sure it is not damaged on the way to the kiln.  Bone dry pottery is then fired for the first time in the kiln at a lower temperature.  This lower temperature firing is called a "bisque" firing and brings the clay into a durable yet porous state, which is ideal for receiving a wet glaze application. 

Finally, bisque ware is decorated with glaze or slip and then placed in a second kiln to be fired to its maturing temperature.  I take advantage of a few different types of kilns to fire my work, which ultimately impacts how my pots look and feel in your hand or home.  I primarily fire in four types of kilns.

Electric Kiln, Cone 6

Electric kilns are generally the most accessible and frequently used kilns in pottery, especially in small community and home studios in the U.S.  They use electrical resistance to heat the kiln (through a metal heat element), much like a toaster oven, and are made of insulated brick to help build and release heat in a predictable manner. Almost all work is bisque fired in an electric kiln and I will often finish work in an electric kiln as well.  

At the studio where I work, we fire to cone 6, which is a mid-high range temperature for clay maturity.  The clay we work with is stoneware, which is durable and appropriate for items of everyday use.  There are many ways you can decorate pottery at this firing range and there are many beautiful effects you can achieve.  The primary limitation of firing your work in an electric kiln is not being able to as easily control and change the atmosphere inside the kiln.  This mostly pertains to the presence or lack of oxygen during the firing, which impacts the color and properties of the clay body and glaze in the finished work.  That being said, electric kiln results are often very consistent and reliable which makes them practical for most potters and applications.

Gas Kiln, Reduction and Soda Firings, Cone 8-10

Gas Kilns are defined by their use of natural gas or propane as a fuel source to heat the kiln.  Like most kilns, they are made of insulating brick and can range in size from a few cubic feet to 15 cubic feet or larger.  One advantage to using a hydrocarbon fueled kiln is that you can more easily control the atmosphere inside the kiln.  By increasing fuel and decreasing airflow (either by letting less air enter the kiln or, more commonly, by slowing down the escape of air through the chimney of the kiln) you can lower the relative concentration of oxygen in the atmosphere, thereby reducing the pots and/or glazes.  

This means that oxygen is pulled from the clay or glaze and the chemistry inside the work changes.  This brings about differences in color, texture, and gloss in the work - often along a dynamic gradient throughout the kiln.  If the atmosphere is controlled evenly and gradually, this gradient can be less pronounced and similar effects can achieved throughout the kiln.  If heat or oxygen distribution varies through lack of control or by intention, you will get a broader range of effects based on how the kiln is loaded and where individual pots rest within the kiln.

An additional variable that can be added to a gas fired kiln is sodium in the form of salt (sodium chloride), soda ash (sodium carbonate), or both!  Salt is often introduced by "burrito" (a combustable package of salt introduced into the kiln at a particular moment) or by loading a plank and then carefully flipping or tossing the salt in the kiln.  Soda Ash is most often dissolved in warm water and then sprayed into the kiln with some type of pressurized device such as a common garden pump sprayer.  Once vaporized inside the kiln, the sodium reacts with the clay and glaze as it moves through the space following the path of heat.

By making decisions about reduction, sodium introduction, oxidation, and decoration, potters can achieve an enormous amount of variation in their work by firing in a gas kiln.  These techniques often yield extremely variable and dynamic work and require the potter to work with the kiln as a collaborator.  I think this makes the process of firing and making more interesting and I enjoy seeing the unique effects that are produced every time!

Wood Kilns, Cone 10-12

Wood kilns are generally defined by their fuel source - wood!  They are most often built of insulating brick like the other kilns described earlier.  They may also include castable components or even may be built partially into the earth.  There are a multitude of kiln designs (noborigama, anagama, train, rocket, etc.), however; I mostly fire in a train kiln (pictured at the top of the page).

In general, wood kilns are heated from a fire box at one end with a chimney at the far end and wares located in the middle.  In this design, heat and ash are drawn from the fire box and through the wares as heat and smoke move up and out of the chimney.  Kiln design strongly influences the efficiency and rate of fuel consumption as do the techniques used by those stoking the kiln.  Since adding wood to the firebox is not automated or continuous, a group of people must constantly monitor conditions within the kiln and stoke the kiln with wood as needed.  Experience tells the potter much of what they need to know and do in response to what they observe in the behavior of the kiln.  Since wood must be added around the clock, a team of people is needed to fire the kiln.  Firings can be fairly brief for a small rocket kiln but can be days or even a week if firing a larger kiln to higher temperatures.  Wood kilns require experience, teamwork, and communication to fire well!

As with gas kilns, the atmosphere in the wood kiln can be influenced by those running the firing.  Reduction can be accomplished with stoking techniques and/or using the baffle on the chimney to modify airflow.  Sodium can be introduced as well, similarly to how it would be introduced to a gas kiln, although this is less common.  Wood imparts unique decoration by depositing ash on the wares as heat and smoke move through the kiln.  The way the kiln is loaded and fired, as well as the type of wood used as fuel, have the greatest effect on the outcomes of the work produced.  In this way, wood fired work is incredibly unique as it is a direct reflection of those who fed the kiln and the land on which the kiln's fuel grew.  Trees draw minerals and nutrients from the soil, hold them in their tissues, and then those same minerals decorate our pots!

The potential of wood fire is great but so are the risks - so many variables and so many hands at work leave ample opportunity for mistakes, accidents, and misfortunes.  Pots are sometimes crushed during firing or upon removal and cracks and other defects are relatively common.  There is also an enormous amount of work involved in cleaning and finishing pottery after it is done firing, as sometimes glazes run and fuse pots to parts of the kiln or the wadding they rest on.  I think the risk is worth the unique beauty produced, but this type of firing isn't for everyone.

Pit Firing

Pit firing is done in a pit! More or less exactly as you would expect.  The most traditional methods are to literally dig a pit in the ground or build a pyre of sorts above ground where the wood is burned, mixed with the pottery.  I have only done this technique a couple of times and the method we used was as follows:  A shallow pit was built just above ground using cinder blocks on a gravel driveway.  We then laid a shallow bed of wood chips, saw dust, and shavings (usually scrap material from a local maker). Pots are nestled into this bed, packed closely together after having been decorated with oxides and/or salts of various descriptions.  Salts, seaweed, and other organic materials were then added around the pots.  Finally, we carefully stacked wood on top of the pottery - smaller kindling with larger logs on the top/outside.  The wood was lit and allowed to burn out, and then the pots were removed the next day after cooling overnight.

When the wood burns, it vaporizes the organic material (salts, seaweed, banana peels, etc.) and the minerals in those materials flash color on the surfaces of the pots.  Where the pots lay in sawdust or have prolonged contact with burning wood, there are black carbon deposits trapped in the surface of the pot.  These colors, black spots, and empty spaces create beautiful movement and decoration on the pot's surface that tells a story of the firing.  Each firing is unique and unpredictable!  

Although there are cultures and traditions that used variations of this firing method to make pots that are functional for cooking, my pots fired in this way are strictly for decorative use.  This is because the temperatures in the pit fire are hot (1,000 F - 1,200 F or so), but they are not hot enough to vitrify and harden the clay so that it is non-porous.  Therefore, if you were to put water in these pots or eat moist food out of them, they would eventually leak or aggregate bacteria and stains on their surfaces.  Colors and decoration would also fade much more quickly.  I do seal my pots with a protective wax which gives them their sheen, enhances their color, and helps protect them from UV light so they stay vibrant.  They are excellent as display pieces in your home and can be used for holding objects or displaying dried flowers.