In one form or another, kilns have been an integral part of pottery-making for centuries. They are essential tools that transform clay into beautiful ceramic pieces through the process of firing. From ancient civilizations to modern studios, kilns have evolved to cater to various pottery techniques and artistic visions. In this article, we will delve into the world of kilns and explore the ten different types that cater to the diverse needs of potters.
What is a Kiln?
A vital component of ceramics production, a kiln is a thermally insulated heating chamber capable of attaining and sustaining remarkably high temperatures. The kiln's role in the ceramics production process is indispensable as it facilitates the necessary high-temperature treatment, also known as "firing," needed to create the pottery and ceramics you know and love today.
Throughout this firing process, a series of controlled chemical and physical reactions transpire, leading to the transformation of the material. Achieving the right conditions within the kiln is a delicate balance. First, the kiln needs to reach an exceptionally elevated temperature and then retain it consistently. Moreover, there are different kiln temperatures that you need to fire at depending on the material used.
A critical aspect of kiln operation is the skillful management of the heating process. Ensuring controlled, gradual heating is of utmost importance; abrupt increases in temperature or exceeding certain thresholds can compromise the quality of the ceramics. Thus, meticulous control over the temperature rise is essential to produce optimal strength and aesthetic ceramics.
What are Kilns Used For?
Kilns serve a wide array of practical purposes in various industries, including being used for ceramic, glass, metal, or composites. Kilns are also used for drying, curing, annealing, tempering, glazing, quenching, fusing, hardening, and sintering. Among these applications, kilns play a pivotal role in the creation of ceramics by firing (curing) clays to achieve sturdy and intricately designed pieces. Similarly, kilns are used for glasswork, aiding in tasks like annealing, fusing, casting, and slumping or reshaping glass materials.
However, kilns can be used for other purposes such as the transformation of wood into charcoal and the efficient drying of freshly harvested lumber. Beyond these conventional uses, kilns are also utilized for metalworking, lime production, food processing, and even cremation!
But, not every kiln serves the same purpose. There are different types of kilns that you’ll want to look into for your specific goal in mind. That’s why we wrote this article: to help you find what kiln you need.
The Different Types of Kilns for Firing
Below, we’ve highlighted the twelve kiln types that you will run into when shopping for a kiln. Some are contemporary and used consistently in the industry while others are less so but are well-known for their functionality and unique design. Are you ready? Let’s get started!
1. Heat Treating Kilns
Available in multiple configurations, these ovens can handle any type of metal, and just about every annealing, normalizing, or hardening process is necessary. They are available with swing doors or guillotine doors that are constructed with heavy-duty hardware for years of hardworking personal or commercial use. An example of this type of kiln is the Evenheat LB27
2. Dual Media Kilns
Dual media kilns are a new type of kiln intended to provide users with the best benefits of both ceramic and glass kilns combined. These Multi-Function kilns typically combine the following attributes: they are top and side firing, allowing the user to control which element is used for what type of firing. They have a digital controller, and they reach temperatures over 2150F degrees.
Each company building kilns has a different approach to their particular design. Still, for the most part, a multi-function kiln is intended to allow a user to fire ceramics one day, and glass another, delivering high-quality functionality for both. A premium price usually follows for this freedom. An example of this type of kiln would be the Paragon Janus 27.
3. Ceramic Kilns
A kiln intended to function for pottery and ceramics is designed to fire to higher temperatures between 2000F - 2350F degrees, these high temperatures are necessary for firing the clay. Glazes may fire at lower temperatures. In addition, the elements in a ceramic kiln are placed on the sides to heat multiple layers of shelves filled with clay pieces.
In the past ceramic kilns typically used a manual controller, called an infinite switch that delivered either; low, medium, or high heat, but did not allow for the ramp/hold programming necessary for glass. Older styles of ceramic kilns used a “kiln sitter” as their heat control device. That feature basically interrupted the flow of electricity to the elements, shutting off the kiln when it reached your desired temperature. Today, ceramic and pottery kilns come equipped with digital controllers that do the work of controlling the temperature variations and the graduation of heat rates to top target processing temperatures and cooling back to room temperature.
4. Glass Kilns
A kiln intended to function for glass is designed to fire at temperatures up to 1700F degrees, these lower temps are suitable for most glass projects. The elements in a glass kiln are placed in the lid of the kiln, as well as on the sides. The top elements work to radiate heat onto the face of the glass surface, while the side elements radiate heat throughout the kiln, stabilizing the internal temperature. Having top and side elements in a glass kiln keeps temperature differences within a glass project uniform and prevents cracking.
Finally, glass kilns always have a digital controller allowing for multiple ramps and hold segments for heating, cooling, and stabilizing temperatures throughout the firing process. These kilns do not fire hot enough to cure ceramics but are highly able to control the heating and cooling cycles required for glass fusing and slumping techniques. These kilns have flat, open shelves to accommodate glass pieces. An example of this type of kiln is the Evenheat GTS2541
5. Raku Kilns
Raku firing is a unique pottery technique that yields mesmerizing effects on glazes. Unlike conventional methods, Raku involves extracting pottery from the kiln while it's still red hot. The pottery is then placed inside a sealed container, along with flammable materials like paper or other organic materials. When these materials come into contact with the scorching pottery, they ignite, creating a reduction atmosphere within the enclosed space.
This atmosphere produces distinct and captivating patterns on the pottery glaze. To achieve this, a closed container is essential. Anything from a sturdy inverted steel bucket to purpose-built containers can be used, as long as they can withstand the intense heat radiated by the pottery and flames.
The kiln needs to be opened while it's still hot, which makes electric kilns unsuitable due to the rapid temperature change that could damage their components. Instead, gas-burning kilns, particularly those fueled by propane gas, are the preferred choice. Raku kilns come in a myriad of shapes and sizes - from commercially manufactured front-loading or top-loading gas kilns to do-it-yourself setups.
A standout among these designs is the iconic top hat kiln. Its popularity stems from the ease of access it provides. With the hood lifted, artisans can effortlessly retrieve the hot pottery using tongs. This design streamlines the unloading process and adds a touch of convenience to the awe-inspiring art of Raku firing. An example of this type of kiln is the Olympic Raku 23
6. Car Kilns
Among pottery, glass, and metal firing techniques, kiln designs are key. Some feature a fixed base, while others incorporate innovative moving elements.
Car kilns exemplify this innovation, with a stationary chamber and a mobile base. These kilns get their name because they resemble automobiles, enabling items to journey through the kiln on the moving base. This concept is scaled up in tunnel kilns, where pottery, metals, or glass undergoes continuous firing as it progresses through the kiln.
An intriguing variation is the shuttle kiln, boasting doors at both ends. The car base shuttles back and forth, allowing pottery to be loaded, fired during its passage through the kiln, and unloaded conveniently from the opposite side. An example of this type of kiln would be the Olympic 53E Car
7. Electric Kilns
The evolution of electric-powered kilns dates back to the 20th century when they emerged primarily for educational and small-scale artistic purposes–like those found in schools and craft centers. Thanks to the increased dependability since their inception, electric kilns have evolved to be 90 percent of what is used by artists, educators, schools, hobbyists, and mid-level production in most industries.
Over the decades, these electric kilns have undergone substantial improvements in reliability and efficiency, expanding their usage beyond educational settings. Unlike traditional kilns that rely on open flames consuming oxygen, most electric kilns create an oxygen-rich atmosphere. Despite this inherent characteristic, skilled artisans can still manipulate these kilns to achieve a reduction atmosphere by incorporating specific techniques and additives.
8. Gas Kilns
Gas-fired kilns, previously a cornerstone of pottery firing, are still quite popular today because they offer diverse designs that can help shape the final outcome of ceramic creations. These kilns employ either natural gas or propane as their heat source, with each type contributing to distinct firing atmospheres and effects on pottery.
One of the primary gas kiln designs is the updraft kiln, characterized by burner ports located at the base. These ports introduce heat into the chamber, allowing the gas flames to ascend the sides and heat up the pottery within. Updraft kilns often incorporate a "bag wall," a barrier of loosely stacked fire bricks that deflects the flames. This prevents direct contact between the flames and the pottery, thus preventing markings and allowing for controlled firing.
On the other hand, downdraft kilns are also introduced at the base, but instead of a flue at the top, the kiln's structure redirects the heat downward, effectively circulating it back to the pottery. This double-heating process enhances efficiency, making downdraft kilns a preferred choice for many potters.
Both updraft and downdraft gas kilns frequently feature a "sprung arch" design, where a curved arc ceiling, supported by straight walls and base, is enclosed within an iron jacket for structural integrity and protection.
These kiln designs exemplify the intricate interplay of heat, oxygen, and pottery materials during firing. Whether utilizing updraft kilns with their bag walls or harnessing the efficiency of downdraft kilns, potters have the flexibility to create diverse and captivating ceramic works. Both downdraft and updraft kilns require appropriate safety controls gas leakage and monitors for carbon monoxide to ensure all safety protocols are followed per state guidelines. A great example of an updraft kiln with safety features is the Olympic 2331G
9. Chamber Kilns (Top Load / Front Load)
Intermittent kilns known as chamber kilns provide a unique firing environment for ceramics. These kilns consist of a thermal chamber enveloping the firing surface, where the ceramic wares are carefully positioned prior to firing. To commence the firing process, the kiln is securely sealed using a door.
Chamber kilns come in two primary designs: top-loaded and front-loaded configurations. The placement of the door dictates the loading style. In the top-loaded variant, the door is positioned on the top of the kiln, allowing for convenient loading from the top. Conversely, the front-loaded version features a door on the front side, necessitating the insertion of wares through the front opening. An example of a Front Load chamber kiln would be the Paragon Dragon 24.
These kilns offer a controlled environment where temperature and atmosphere can be precisely regulated to achieve desired firing outcomes. The chamber design facilitates uniform heat distribution, contributing to consistent firing results across all loaded wares.
Unlike continuous kilns, chamber kilns require periodic reloading and unloading since they operate in batches. This characteristic can be advantageous for certain artistic or specialized endeavors that require more customization, allowing artisans to have more direct control over the firing process.
Furthermore, the modular nature of chamber kilns enables easy expansion and adaptation. Kiln components can often be customized and rearranged to accommodate larger or differently shaped pieces. This flexibility contributes to their popularity in various artistic and small-scale industrial settings. An example of a Top Load chamber kilns would be the Cress 2818E
10. Beehive Kilns
The Beehive kiln stands as one of the earliest kiln types known. With a distinct appearance reminiscent of the upper part of a beehive, these kilns found their purpose in large-scale pottery manufacturing, characterized by their substantial brick constructions.
These kilns boast a unique structure: a circular, stout body with straight walls accompanied by a gracefully curved domed roof. Beehive kilns were crafted in both downdraft and updraft configurations.
The layout and design of larger Beehive kilns typically followed the downdraft model, incorporating a chimney. These kilns functioned by introducing fuel into a firebox positioned beside the kiln. The resulting heat penetrated the kiln and ascended, guided by a bag wall. Upon reaching the enclosed ceiling, the heat was compelled to descend again, creating a cyclic circulation.
Effluents and heat exited the kiln through a subterranean flue in the floor, progressing through an underground path until reaching a distinct chimney situated apart from the kiln.
Conversely, simpler Beehive kilns embraced an updraft layout. Within these kilns, heat ascended through the structure and exited via a short flue positioned atop the kiln. Interestingly, this design bears a resemblance to another early kiln type known as the bottle kiln. The similarities between these two designs occasionally lead to the interchangeable use of the terms "beehive" and "bottle" kilns. It's worth noting, however, that nuanced differences do set them apart.
11. Soda Kilns
Much like wood-burning kilns, soda kilns are constructed using bricks and often offer ample space for walk-in access. These kilns commonly feature a distinctive architectural layout, adopting a sprung arch or catenary arch design, complemented by a chimney positioned at one end. Typically, soda kilns are fueled by natural gas, though some variations are wood-fired to infuse unique qualities into the pottery.
During the firing process, a sodium solution is introduced into the kiln, a pivotal step in soda firing. This injection usually occurs around the point where the kiln's temperature reaches approximately 2336°F (1280°C), equivalent to cone 9 temperature, making soda firing well-suited for stoneware ceramics. The sodium solution, created by dissolving sodium bicarbonate in water, transforms into vapor upon release. This vapor envelops the pottery, interacting with the clay to create an alluring glaze.
The resulting glaze often exhibits a distinctively textured appearance resembling an orange peel's dimples. Characterized by intriguing shifts in color and tonal variations where the sodium solution makes contact with the pottery, this phenomenon is aptly referred to as the "flashing effect."
Interestingly, soda kilns deviate from conventional door designs. Instead of a hinged door, these kilns are sealed at the entrance using bricks for each firing cycle. The sodium solution enters through a specially designed hole in the 'door,' which is essentially a bricked-up opening with a strategically removed brick. After firing, once the kiln has cooled over a span of several days, the 'door' is meticulously dismantled, brick by brick, revealing the artistic outcomes of the soda firing process.
12. Top-Hat Kiln (Also Known As Bell Kiln)
The top hat kiln introduces a unique approach to ceramic firing. In this method, ceramic wares are positioned on a firing surface atop a hearth or plinth. The distinctive feature is the 'hat'—a box-shaped cover that encloses the wares before firing, lending an element of precision and control to the process.
What sets top hat kilns apart is their adaptability to various energy sources. They can be fired using natural gas, LPG, diesel, kerosene, other liquid fuels, or electricity. This flexibility lets artisans tailor their firing techniques to suit the specific preferences and needs of their ceramic creations. An example of a bell kiln is Olympic’s GF32E.
Kilns come in many shapes and sizes, each serving its own function. The type of kiln that you buy ultimately comes down to what you’re looking to do. Kilns often fit into multiple categories at once, so understanding the categories, what they mean, and the types of kilns available will help buyers make wise purchasing decisions. If you’ll be handling a significant amount of metal, then a heat-treating kiln might be best for you, but a kiln that goes to heat-treating temperatures that have the right configuration for your projects could be a better fit. Hopefully, this guide helps you make that choice. Similarly, if you want to do raku pottery, then a raku kiln is what you want so you can get the unique designs that you’re looking for.
Feel free to check out our wide array of kilns available here at KilnFrog; and if you have any other questions, reach out to us! Happy firing.