The Orton Foundation proudly supports the National K-12 Ceramic Exhibition.
The K-12 Ceramic Foundation fosters support and nurtures creativity...
NCECA - Virtual May 2021
PowderMet 2021 - Hybrid Format - Orlando, FL June 20-23, 2021
Ceramics Expo - Cleveland, OH August 31- Septermber...
Understanding creep behavior provides insights for design improvements and quality assurance.
To see the Case Study, Click Here
Orton is pleased to announce its partnership with Hot Disk of Gothenburg, Sweden representing Hot Disk in the Eastern United States, as well as Central and South America. Mr. Jim Baldwin is the Product Manager for Hot Disk and brings over 30 years experience to manufacturing, sales and service of thermal lab equipment. Hot Disk Instruments measure thermal conductivy, thermal diffusiviy and specific heat of any kind of solid or liquid material. To see the complete line of Hot Disk products, you can visit our Hot Disk page HERE.
To reach us by email CLICK HERE or call us at 614-818-1330.
Orton has partnered with Zonos so Customers around the world can order small quantites of Orton products and determine the total delivered cost before placing the order. The price shown will include the product, shipping, duties and taxes if applicable. Depending on the country, there are normally different levels of services to choose from.
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Do cones have a shelf life?
At the Edward Orton Jr. Ceramic Foundation, a common question asked to us by ceramic artists, potters, or engineers is whether cones have a shelf life. Are cones still usable when they are old? The answer is most always yes, if cones were stored in a dry location, they will still work. The materials used to form cones will not change with age. They are clays, and inorganic minerals that have been mined and refined to make them powdery, like flour. They are blended, mixed with water and binder and pressed into the shape of a cone. We know that the materials remain unchanged since they had been sitting stable and unchanged in the earth’s crust long before they were mined. It is logical that they would also remain unchanged now that they are in the form of a cone.
Having said that, a call occurred last week from an artist saying she found an old box of our Large pyrometric cones labeled 010, and asked if we wanted it (figure 1).
Figure 1- Large Pyrometric Cones 010
She thought it would have some historical importance to Orton. She sent us the box , and it still contained all 50 cones. The thought then occurred to me that I could use them to confirm our response on this subject. I decided to compare them to cones we make today. Every box of Orton cones shows the cone number identified on the box, but each box is also marked with a batch code. This box was marked with the code 114/2, (Figure 2).
Figure 2 - Bottom of box showing batch code 114
Now, when I started work at Orton nearly 20 years ago, I inherited from the previous ceramic engineer, production records for cone batches produced during the 44 years he worked at Orton. Those records were passed on by the engineer who preceded him. I have continued this practice and will be passing my records to the next engineer. In all, I have records dating as far back as 1911. Using these records, I found the batch record for cone 010, lot 114, (figure 3).
Figure 3 - Cone 010 Batch record dated December 1959
It was dated December 1959. Some additional history, back then, The Orton Foundation was located at 1445 Summit Street Columbus, Ohio (figure 4).
Figure 4 - Orton Memorial LaboratoryAt that time, large cones were made using wet clay that was pressed into a plaster mold. A process that worked well, but was labor intensive and required a lot of energy to dry the plaster molds as well as being time consuming.
In 1970, Orton started their move to our current location in Westerville. The move allowed Orton to update the way we made cones to a more modern technology, using a semi-dry press process that involves pressing cones in metal dies under high pressure. This method is more efficient and produces cones faster, with less energy, and with a more uniform shape.
I thought it would be interesting to see how the 1959 cones perform when fired along with cones we make today. But, since I like to make things complicated, (an engineer to the end), I also gathered cone samples from the time I began at Orton in 2001, some cones made this year, our Orton Standard Cones and cones from the 1959 box and fired them together.
Now, I think it is important to clarify what is meant by Orton Standard Cones.
Cones had been made by Edward Orton Jr. since 1896. He originally called his company The Pyrometric Cone Company and always wanted to make cones of the highest quality. When he passed in 1932, he wrote into his Will that the Cone Company would continue as a non-profit trust called The Edward Orton Jr Ceramic Foundation. Under the leadership of the board of trustees, who were appointed to oversee the Foundation, they decided to send Orton Cones to the National Institute for Testing Materials (N.I.S.T.). At NIST, they tested the cones and established them as standards. This research was published in the American Ceramic Society Journal Volume 39, 1956. Any batch of Orton cones made from them on would be compared to that set of standard cones to insure they remained as accurate as possible.
Now, we test every batch of cones at up to three different heating rates using Orton Standards to confirm they are accurate and precise.
The result from my experiment was affirming, as seen in Figure 6. The cones made in 1959 fire the same as the cones made 20 years ago as well as those made this year.
Figure 6 - 1959 era cone (far right) next to Orton Standard, 2020 cone, 2001 cone (far left)
It is always good to review, and it also never hurts to look back at history. We continue to make millions of Orton Standard pyrometric cones to the same level of precision and care as Edward Orton Jr.
Our customers understand using pyrometric cones to confirm their ceramic firings, translates into producing quality ceramic ware. Yes, if you keep them dry, cones have a long shelf life. But please, don’t let them sit on a shelf and gather dust!
Verifying temperatures in your Sintering Furnace? The August Buyers Guide of LMT magazine offers TempTab as a solution. Please click on the link below for more information:
The Ohio State University College of Engineering Department of Materials Science and Engineering and The Edward Orton Jr. Ceramic Foundation are sponsoring a Workshop June 18th & 19th, 2019 in Columbus, Ohio. The event will include Technical Presentations, Workshop Discussions, Networking events including Dinner and a Tour of The OSU CEMAS Center for Electron Microscopy and Analysis. CLICK HERE for a copy of the Program and Workshop Details.
In response to industry demand, Orton is offering a series of new short courses dealing with refractories and glass. The first new course to be offered is "Advanced Thermal Properties of Refractories,” to be held on October 29 and 30, 2018 in Columbus, Ohio. In addition to the above advanced course, there will be two other advanced courses, three technician training courses, and a new introduction to glass course offered in the future.
The tentative course schedule with dates is shown below:
Technician Training – Thermal Properties of Refractories (March 2019)
Advanced Mechanical Properties of Refractories (June 2019)
Technician Training – Mechanical Properties of Refractories (October 2019)
Technician Training – Physical Properties of Refractories (March 2020)
Introduction to Glass (March 2020)
Introduction to Refractories (June 2020)
Technician Training – Thermal Properties of Refractories (March 2021)
Advanced Corrosion Behavior of Refractories (June 2021)
Technician Training – Mechanical Properties of Refractories (October 2021)
Each course combines both classroom and practical lab experience.
Orton will provide certificates for students completing a combination of three advanced courses or three training courses plus one introductory course.
For Additional Questions Concerning the Courses Contact
Dr. Joseph Homeny
The Edward Orton Jr. Ceramic Foundation
Phone: (614) 818-1323
About The Edward Orton Jr. Ceramic Foundation
The Standard Pyrometric Cone Company was established in 1896 by Dr. Edward Orton Jr., the first Chairman of the Ceramic Engineering Department at The Ohio State University. With the creation of the Edward Orton Jr. Ceramic Foundation after his death in 1932, the primary focus became providing products to assist and enhance high-temperature processing of ceramics and other materials. Today, Orton provides Pyrometric Devices, Thermoanalytical Instruments, and Material Testing to more than 70 countries worldwide.
Learn more about Orton Ceramics here.
Measuring Flexural Creep of Ceramic Investment Casting Shells
Understanding the creep behavior of the ceramic shell is important because shell distortion at high temperatures must be minimized during the metal casting process.
Read the rest of this article here: ceramicindustry.com
5 Ceramic Products That Changed the World!
When you think of ceramics, many people may flash back to a high school pottery class or think of a fine china or dollmaker. What many do not realize is that we use ceramics for everything from screws to laboratory equipment. Working directly with our customers, Orton continually explores new products and services with the same commitment our founder Dr. Edward Orton Jr. made to the ceramic industry over 100 years ago. The ceramic industry is vast, creating products used by everyone in the world. There are some that you might not think of, though, and we want to show you some of the more interesting items on the list to broaden your view on the wide world of ceramics. It is so much more than your mom’s favorite vase.
1. Ceramic Dental Products
The color, size and strength of dental parts made from zirconia are directly related to the temperature they are sintered. The fascinating use of ceramic in the dental field seems tailor-made. Ceramic is the proper color, consistency and general feel of natural teeth. Being that it is ceramic material, the temperature can be set so precisely that the ceramic hardens into the exact hardness of human teeth. Interesting fact: Before the use of ceramic in dentistry, materials such as wood, wax, gold, silver, plastic and even seashells! For more interesting stories of wild things people used to do with their teeth in history, click here.
2. Jet-Engine Turbine Blades
I bet you didn’t know that ceramics are used in the turbine blades for jets! That’s right, while often mixed with an alloy into a composite, ceramics are used in aircrafts because they are ⅓ the weight of an alloy, they can operate under degrees of 500 or higher unlike alloys which will soften with intense heat, they increase thrust due to not needing as much cooling air, reduce gas consumption and reduce the cost of electricity. Technologies like ceramic composites are making our aircrafts more efficient, lighter, faster and stronger.
3. Space Shuttle Tiles
Did you ever wonder how they were able to make space shuttles that do not burn up on re-entry to Earth’s atmosphere? The answer? Ceramics! Ceramics can handle such high temperatures that when scientists from shuttle development placed a sample of the ceramic shuttle tiles into a 2200 degree furnace. When taken out, they could pick the tiles up in less than 10 seconds with their bare hands while they still glowed, molten inside. The science of ceramics not only helps us get to space, it allows us to get home and share the story. To see the video of the glowing shuttle tiles, click here!
4. Ballistic Protection
Why would body armor be made with ceramic plates? Hard body armor, made out of thick ceramic or metal plates, functions basically the same way as the iron suits worn by medieval knights, the armor material pushes out on the bullet with the same force with which the bullet pushes in, so the armor is not penetrated. You may be thinking, bathroom tile is made of ceramic and it is extremely brittle, so how does it work against a bullet? It turns out there are thousands of different materials classified as ceramics. The ceramic used in body armor is called alumina, with the chemical formula Al2O3. Sapphires are made of alumina, and sapphire is very strong.
5. Biomedical Implants
Over the last twenty years, there has been a considerable increase in the use of ceramic materials for implant devices. With an excellent combination of strength and toughness together with bio-inert properties and low wear rates, a special type of oxide called zirconia is now used for total hip replacements. The zirconia doubles the strength of implants prompting other applications which could benefit such as knee joints, shoulders and spinal implants. Just like with teeth, ceramics can be made to closely resemble bone in weight, density, color and strength.
Ceramics Are Cooler Than Your Pottery Class...
Ceramics are changing manufacturing and technology more every year. The breakthroughs in composites and temperature testing are creating safer, stronger, better and more advanced products than ever before. There are so many more interesting uses for ceramics today. To learn more, visit Orton Ceramics online at www.OrtonCeramic.com. You can also get to know us better by liking our Facebook page to receive more access to our great articles, posts and updates! Visit us on Facebook and Twitter at @OrtonCeramic.
The Board of Trustees of the Edward Orton Jr. Ceramic Foundation announces the retirement of its General Manager for the past 16 years, Gary Childress effective February 2, 2018. Mr. Mark Lawson will replace Mr. Childress as General Manager.
Mr. Lawson joins Orton following more than 20 years in senior management positions with Elkay Manufacturing, Trigon International and Tervis. Mr. Lawson has a BS degree in Mining Engineering from Virginia Polytechnic Institute, a Master’s degree in Materials Science and Engineering from the University of Pittsburgh, and an MBA from the University of Chicago. Mr. Lawson’s education and experience in materials will add significant value to the leadership of the management team of Orton.
Those experienced in firing ceramics know that kiln atmosphere can have a major influence on the reaction rates and properties of the ware. Since the point at which a cone will bend is brought about by thermochemical reactions, we would also expect that atmosphere also influences when a cone will deform. Fortunately, the atmospheric conditions that influence product properties generally have related effects on cone behavior.
The appearance of cones after they have been drawn from the kiln usually gives an indication of the kiln conditions during the progress of the cones through the fire. Cones going down in the wrong sequence or direction are often an indication of improper placement of the cones, improperly made plaques used to hold the cones, or some other atmospheric effect.
The environmental conditions that are most likely to influence cone behavior are listed below followed by a short description of the cause:
Presence of sulfur gases
Presence of water vapor
Drafts within the kiln
Reducing conditions are associated with gas kilns when the ratio of gas to air is adjusted so the oxygen content is very low. Under reducing conditions, the organic binder and any organic matter associated with the materials used in making a cone, cannot fully oxidize. As a result, the cones will develop a black core from trapped carbon. Most ceramics will mature at lower temperatures when fired in a reducing atmosphere.
In some processes, excess fuel is injected into the kiln to induce reduction, as is commonly done in the manufacture of bricks to produce a color effect. This process often called “Flashing” does not normally have an adverse effect on cone deformation.
Black coring can also occur if the temperature is increased too fast at the onset of a firing. Under such conditions, there is insufficient time for oxidation of the organic material within the cone to occur.
The presence of a carbon core (black coring) can induce bloating and change the bending behavior of a cone, making them inaccurate.
Typical appearance of cones
Cones exposed to reducing atmosphere
The presence of sulphur in kilns will have an adverse effect on cones that are manufactured with red iron oxide; those include cones numbered from 010 to 3. The “red” cones will have a green to black appearance after firing in a reducing atmosphere.
In kiln atmospheres that are either Sulphurous or reducing, cones can also develop a rigid “shell” with a softened interior that is partially melted. These “Hard-shelled” cones will not deform naturally. The surface of the cone will have a matte finish and appear rough with sharp edges. Hard-shelled cones do not bend in an arc but are stiff and will bend only at the base, like a felled tree. Hard-shelling may also be encountered due to the volatilization of boric oxide from the glass frit used to manufacture cones numbered from 010 to 3. Hard Shelling causes cones to deform at temperatures higher than normal.
In order to provide cones that will work in reducing conditions and in the presence of sulphur, Orton manufactures a twin line of cones that are formulated without red iron oxide. The “Iron free” cone series is identical in performance to the regular series of cones from 010 to 3.
The presence of water vapor, particularly in larger quantities, will influence cone behavior. The action of water vapor upon a cone will make it deform sooner than normal. The reason for this is that water vapor diffuses into ceramic materials and causes changes in the vitrification process. This accounts for different behavior seen in firings made in an electric kiln as compared to a gas fired kiln. Even though water vapor in the products of combustion can run as high as 20%, it does not take away from the value which cones can have because comparable effects are usually found in the properties of the ware.
Fly ash from the burning of solid fuel may settle on cones and influence thier deformation.
Likewise, volatile products such as salt fumes, lead, and zinc compounds may produce a surface glaze on the cone which may influence cone bending behavior.
The cutting tongues of flames may cause cones to develop melted tips, or cause abnormal deformation if the cones are placed too close to gas burners. If possible, cones should be protected from flame impingement and kiln drafts.
Radiation from hot surfaces, or, if the cones are placed close to cooler surfaces, will have some effect on cone deformation, and, so far as is practical, should be protected from such conditions.
Cone exposed to Flame Impingement
Radiant effect on cone to the right
From the above examples, it is evident that one can critically analyze kiln conditions through careful observation of the pyrometric cones drawn from the kiln. A properly responsive set of cones will invariably indicate a properly fired kiln, provided the heating schedule is suited to the ware.
More Information on Pyrometric Cones
For more information on Pyrometric Cones, refer to Orton’s website - Click Here
Have A Question?
If you have a question about Pyrometic Cones, Temperature Verification or Anything Else, Contact Our Team Here: Contact Orton Here
TempTabs are used to measure temperature uniformity, consistency and repeatability in high temperature applications between 850-1750C (1560-3180F). Learn More Here:
The Edward Orton Jr. Ceramic Foundation is pleased to announce that Dr. Joseph Homeny has been promoted to Research and Technical Director. Dr. Homeny joined Orton in 1992 as Manager of Orton’s Testing Services and has lead the development of Orton’s Testing Services to a highly respected and trusted testing services laboratory, supporting the ceramic industry with trusted and unbiased material analysis data. Dr. Homeny received his PhD in Ceramic Engineering from the Pennsylvania State University in 1980.
Mr. Brian Rayner has been promoted to fill Dr. Homeny’s position of Testing Services Manager. Mr. Rayner joined Orton in 2004 and served as a Materials Testing Engineer and most recently as Laboratory Manager. Mr. Rayner received his BS degree in Ceramic Engineering from The Ohio State University in 1998.
Dr. Beau Billet has been promoted to Laboratory Manager. Dr. Billet joined Orton in 2016 as a Materials Testing Engineer. Dr. Billet received his PhD in Materials Science and Engineering from The Ohio State University in 2013.
Orton expanded its Testing Services laboratory space in 2016 with the addition of an 8,000 square foot building, emphasizing Orton’s commitment to providing unsurpassed services to the ceramic industry.
The Edward Orton Jr. Ceramic Foundation was established as a Trust under Ohio statutes in 1932. Orton provides pyrometric devices to verify thermal processing, electronic kiln controllers, thermo-analytical instruments to measure high temperature properties of ceramic materials and laboratory analysis of materials based on ASTM Standards. All profits from the operations of Orton are utilized to support research at the university level in support of the ceramic industry.
Controlling the temperature when sintering dental zirconia crowns, veneers, and implants is critical in order to achieve the highest quality.
The color, size and strength of dental parts made from zirconia are directly related to the temperature they are sintered. The target temperature required to properly sinter Zirconia does not allow for much error. Without proper control of the temperature, all of the detail and workmanship put into the parts can be ruined if placed into a poorly controlled furnace. Control is achieved through the use of electronic temperature controllers, thermocouples and calibrated shrinkage products (TempTAB®).
Electronic controllers are basically volt meters. They convert the millivolt signal generated from the thermocouple into a temperature. Extra computer logic is added along with some hardware to make the controller do some additional tasks to heat and cool the furnace on a programmed heating cycle. To perform properly, the electronic controller has to be calibrated. This is not a one-time thing. Electronics degrade over time and require service to compensate for the degradation. If not accounted for, a controller can easily misreport the actual temperature by as much as 50 degrees C. Check your owner's manual and contact your furnace supplier to find out how to calibrate the furnace according to their recommendations.
Thermocouples are made from two dissimilar metallic wires that are welded together to form a bead. When the bead is heated, a very small electrical signal is generated in the wires. The electrical signal is on the order of millivolts and can be detected by connecting the ends of the wires to a volt meter (electronic controller). Since the wire used to form a thermocouple degrades with each thermal cycle, the small electrical signal it generates will change as well. Over time the signal will degrade to the point where the temperature read by the electronic controller will no longer be accurate. The furnace readout will continue to display a temperature value, but the actual temperature can be off by over 100 degrees.
To help the operator monitor the accuracy and repeatability or the furnace, they can place a calibrated shrinkage product into the furnace. The TempTAB 700, produced by Orton, is just such a device. The TempTAB 700 is made to be sintered along with the Zirconia parts. The operator will measure the diameter of the TempTAB after the thermal cycle is complete and input the measured value into the TempTracker software program. Orton engineered the TempTAB 700 so that the shrinkage can be converted to a representative equivalent sintering temperature. By using the TempTAB on a regular basis,( daily or weekly) the operator can determine when the thermocouple and electronic controller begin to degrade and insure that the zirconia reached the proper sintering temperature.
Since the TempTAB do not rely on an electrical signal that can change with each cycle, they can be trusted to provide a real measurement of the temperature seen within the furnace. By using the control chart generated by the free TempTracker software, the operator can see when it is time to either replace a thermocouple, or call for calibration service. The best time to begin using the TempTAB is immediately after a calibration or at the start of using a new furnace to establish a benchmark for future comparison.
This video highlights the award winning pieces of miniature ceramic art from the 2016 Orton International Cone Box Show displayed during NCECA 2016 at the Hilliard Gallery in Kansas City, Missouri.
Refractories can be evaluated after their service life to collect critical information that may be used to guide product development and lead to improvement in performance. Evaluation may be conducted after years of service or immediate after a catastrophic failure. Evaluation of a used refractory material may include chemical analysis, measurement of physical properties, measurement of mechanical properties, and/or examination of the refractory microstructure. The American Society for Testing and Materials (ASTM) provides many standard procedures for measuring these properties.
Chemical analysis of refractory materials is typically accomplished through a combination of X-Ray Fluorescence (XRF) and Inductively Coupled Plasma (ICP). A common approach is to analyze the chemistry of the hot face or affected area and the cold face or unaltered area. A representative sample is cut from the refractory and ground into a powder specimen. The specimen is prepared further in the laboratory for analysis. With knowledge of the chemistry, it may be possible to determine what might be affecting the refractory while it is in service.
Physical properties that are commonly measured include percent porosity, bulk density, reversible linear expansion behavior, permanent linear expansion, pyrometric cone equivalent (PCE), permeability, and abrasion resistance. Again, specimens from the hot face or affected area and the cold face or unaltered area are typically measured and compared. If a cold face or unaltered area is not available, it is preferred to measure unused material. In the event that unused material is not available, measured data can be compared to the manufacturer's data sheet. From the measurement of physical properties, it may be possible to determine if the service conditions are affecting the refractory, if the refractory was manufactured properly, or if the refractory was installed properly.
Mechanical Properties that are commonly measured include flexural strength, compressive strength, and creep behavior. Flexural and compressive strength may be evaluated at ambient or elevated temperatures. The creep behavior may be measured using different test temperatures, stresses, and loading types (compressive or flexural). From the measurement of mechanical properties, it may be possible to determine if the service conditions are affecting the refractory, if the refractory was manufactured properly, or if the refractory was installed properly.
In some cases, particularly if corrosion is suspected, it may be beneficial to closely examine the refractory microstructure. Optical and/or scanning electron microscopes (SEM) are typically utilized. Specimens from the hot face or affected area and the cold face or unaltered area are typically examined. Electron microscopes equipped with energy dispersive spectrometer (EDS) can collect chemistry data and this information can be overlaid on the image to produce chemistry maps.
Refractory post-mortem analyses provide valuable, technical information. This information can lead to enhanced refractory properties through research and development, process changes, or design changes. Furthermore, this information can lead to reduced downtime, longer refractory, life, and more efficient processes.
If you have questions about this event or any of our other products Call Us: 614-895-2663 or Contact Us by Clicking Here
The Orton Cone Box Show will be featured during the 50th Anniversary of the NCECA (National Council on Education for the Ceramic Arts) Conference at the Hilliard Gallery, 1820 McGee Street, Kansas City, MO. Jurors will be Greg Daly, Garth Clark and Inge Balch.
The show runs from March 4th through the 19th a and on the NCECA bus tour. The pieces in the show will be available for sale and can be picked up after March 19th. Entries from past jurors will also be included in the show. Pieces from Bede Clarke, Jeff Oestreich, Phil Rogers, Nina Hole, Richard Notkin, Steven Hill, Harris Deller, Anna Holcombe, John Neely among others will be on display. The "opening evening" will be Friday March 18th from 5 to 9pm. All pieces in the show must fit into a 3" x 3" x 6" Orton Standard Pyrometric Cone Box.
To Learn More about the Cone Box Show - Click Here
Here are some previous entries:
"No More Lenore" by Tammie Rubin Champaign, IL USA www.tammierubin.com
"Portrait of John at Orton" by Claire Salzberg Westmount, Quebec CANADA www.clairesalzberg.com
If you have questions about this event or any of our other products Call Us: 614-895-2663 or Contact Us by Clicking Here
Orton has pyrometric products, electronic controllers and kiln vents for monitoring and controlling your electric and production kilns.
For most of the ceramic community, whatever happens inside a kiln as it heats our ware is a mystery. The kiln is not clearly understood. It is considered a black box that somehow takes our clay pieces and transforms them into something more permanent.
Heating is required for ceramic or glass products. The kiln provides the heat necessary to properly develop the properties - color, finish, durability, etc. Here, I will try to explain the concept of how an electric kiln transfers heat inside the kiln into the ware.
Heat can come from passing electricity through a wire or a heating element, which in turn gets hot and transfers heat to its surroundings.
The way that the heat is transferred occurs in three ways:
1.Convection 2. Conduction 3.Radiation
Convection is the first way heat is transferred in the heating process. As air is heated inside the kiln, it passes across the warming heating elements. Hot air will rise and cool air will be heavier and fall toward the bottom. As this occurs, air currents will begin to circulate and bring hot air to cooler places in the kiln. The temperature inside the kiln at this early stage of the firing will not be uniform unless the air is pushed through the kiln. Most low temperature cone firings, such as 022 to 016 depend more heavily on convection for heat transfer. These include firings for glass processing, decals, decorative lusters (mother of pearl, gold), and low fire bisque.
Conduction occurs when heat moves through a solid. An example would be how heat moves from a saucepan into the handle. This is a slower process of heat movement as the transfer of heat is dependent on the ability of the material to transmit heat. The measurement of how well a material transmits heat is defined by a term called thermal conductivity.
In a kiln, conduction of heat moves from the inside to the outside of the kiln and from the outside to the inside of the ware. Conduction is the main mechanism for getting the temperature uniformly distributed throughout the kiln. This is why soaking the kiln at a set temperature is so effective. This is a slow process and if the firing is too fast, the inside of the ware will not receive enough heat to fire properly.
Radiation starts to occur at the beginning of the firing, when the elements are the hottest part of the kiln. The heat from the elements radiates out like the sun warming us on a cool day. Eventually, the firebrick, kiln shelves, and the ware will also get hot and begin to radiate heat. As the temperature increases, more and more of the heat is transferred by radiation from the heating elements. For uniform heating, it is important that all surfaces of the ware be exposed to the heating elements, even partially. If large items are placed in front of smaller items, the large items will act is if they are trees shading us from the sun.
Temperature Uniformity within an electric kiln is best achieved by loading the ware so that the heat can penetrate all areas. The hot air and the items getting heated by radiation warm the surface of the ware. Sufficient time is needed to move the heat to the ware and into the ware.
Unless the heat is moved by mechanical means, the hot air will rise to the top of the kiln and the cooler air will fall to the bottom. A difference of two cone numbers can be seen if firing to a low temperature such as between cones 022 to cone 016. Use of a downdraft kiln vent will promote the distribution of the warm air at low temperatures when heat is moving by convection. Downdraft venting helps to counteract the effect of rising heat bringing the warmer air down to the cooler bottom of the kiln.
Soaking or holding the kiln at a temperature can help equalize heat, but truly uniform conditions will not naturally occur until higher temperature, where radiation is more effective. Electronically controlled kilns are capable of being programmed to include a hold at a desired temperature.
Heat moves through ware from the outside to the inside. It is important to try to uniformly heat all surfaces of the ware. How you load the kiln can help to promote even heating. Firing slower also allows for the heat to penetrate to the inside of the ware.
If the top of a piece is heated, but the bottom is touching a cool shelf, the item may crack or warp as one surface is heated more rapidly than the other. This is why it is important to use plate or tile setters for large flat objects.
The practice of nesting bowls or cups in bisque firings is discouraged, as this will prevent the inside of the ware from heating at all, and will restrict heat from moving into the inside of pieces, or the inside of the bottom piece. It is better to invert them and/or place these items rim to rim.
It is also important to make sure larger items do not block smaller ones from the heat source and that the ware is placed at least one inch away from the hot elements. Ware placed too close to the elements may distort or glazes and colors may not develop properly.
Placement of Orton Self-supporting Pyrometric Cones throughout the kiln will serve as an indication that the heat has penetrated the ware and by visual inspection of the degree of bend; will indicate the uniformity of the firing. Use of an electronic temperature controller, like the Orton Autofire®, will insure the kiln is firing on a controlled heating rate as well as provide the ability to hold the kiln at a temperature long enough to even out the temperature as heat moves by conduction. Coupled with the Orton Vent Master® downdraft vent, and employing the knowledge of how heat is transmitted through the ware, temperature uniformity can be achieved.