Pyrometric cone
Encyclopedia
Pyrometric device
Pyrometric devices gauge heatwork when firing materials inside a kiln. Pyrometric devices do not measure temperature, but can report temperature equivalents...
s that are used to gauge heatwork
Heatwork
Heatwork is the combined effect of temperature and time. It is important to several industries:*Ceramics*Glass and metal annealing*Metal heat treating...
during the firing of ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
materials. The cones, often used in sets of three as shown in the illustration, are positioned in a kiln
Kiln
A kiln is a thermally insulated chamber, or oven, in which a controlled temperature regime is produced. Uses include the hardening, burning or drying of materials...
with the wares to be fired and provide a visual indication of when the wares have reached a required state of maturity, a combination of time and temperature. Thus, pyrometric cones give a temperature equivalent, they are not simple temperature-measuring devices.
The pyrometric cone is described by Dodd and Murfin (1994) as A pyramid with a triangular base and of a defined shape and size; the "cone" is shaped from a carefully proportioned and uniformly mixed batch of ceramic materials so that when it is heated under stated conditions, it will bend due to softening, the tip of the cone becoming level with the base at a definitive temperature. Pyrometric cones are made in series, the temperature interval between the successive cones usually being 20 degrees Celsius. The best known series are Seger Cones (Germany), Orton Cones (USA) and Staffordshire Cones (UK)'.
Usage
For some products, such as porcelain and lead-free glazesCeramic glaze
Glaze is a layer or coating of a vitreous substance which has been fired to fuse to a ceramic object to color, decorate, strengthen or waterproof it.-Use:...
, it can be advantageous to fire within a 2-cone range. The 3-cone system can be used to determine temperature uniformity and to check the performance of an electronic controller. The 3-cone system consists of three consecutively numbered cones:
- Firing Cone - cone recommended by manufacturer of glaze, slip, etc.
- Guide Cone - one cone number cooler than firing cone.
- Guard Cone - one cone number hotter than firing cone.
Additionally, most kilns have temperature differences from top to bottom. The amount of difference depends on the design of the kiln, age of the heating elements, load distribution in the kiln, and the cone number to which the kiln is fired. Usually, kilns have a greater temperature difference at cooler cone numbers. Cones should be used on the lower, middle and top shelves to determine how much difference exists during firing. This will aid in the way the kiln is loaded and fired to reduce the difference. Downdraft venting will also even out temperatures variance.
Both temperature and time and sometimes atmosphere affect the final bending position of a cone. Temperature is the predominant variable. We refer to the temperature as an equivalent temperature, since actual firing conditions may vary somewhat from those in which the cones were originally standardized. Observation of cone bending is used to determine when a kiln
Kiln
A kiln is a thermally insulated chamber, or oven, in which a controlled temperature regime is produced. Uses include the hardening, burning or drying of materials...
has reached a desired state. Additionally, small cones or bars can be arranged to mechanically trigger kiln controls when the temperature rises enough for them to deform. Precise, consistent placement of large and small cones must be followed to ensure the proper temperature equivalent is being reached. Every effort needs to be made to always have the cone inclined at 8° from the vertical. Large Cones must be mounted 2 inches above the plaque and Small Cones mounted 15/16 inches. With the cones having their own base "Self-Supporting Cones" eliminates errors with their mounting.
Reference tables for the temperature equivalents for a number of different Pyrometric cones can be found through links in the 'External Links' section.
Control of variability
Pyrometric cones are sensitive measuring devices and it is important to users they should remain consistent in the way that they react to heating. Cone manufacturers operate procedures to control variability (within batches and between batches) to ensure that cones of a given grade remain consistent in their properties over long periods. Whilst there are a number of national standards ISOInternational Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...
have published ISO 1146:1988-02 regarding Pyrometric cones.
Even though cones from different manufacturers can have relatively similar numbering systems they are not necessarily identical in their characteristics. If a change is made to cones from one manufacturer to another than allowances for the differences can sometimes necessary.
History
Archaeologists working at Northern Song period (960 to 1127 AD) kiln sites in the Chinese provinces of ShaanxiShaanxi
' is a province in the central part of Mainland China, and it includes portions of the Loess Plateau on the middle reaches of the Yellow River in addition to the Qinling Mountains across the southern part of this province...
and Shanxi
Shanxi
' is a province in Northern China. Its one-character abbreviation is "晋" , after the state of Jin that existed here during the Spring and Autumn Period....
have reported that pyrometric cones about five centimetres tall and made from loess
Loess
Loess is an aeolian sediment formed by the accumulation of wind-blown silt, typically in the 20–50 micrometre size range, twenty percent or less clay and the balance equal parts sand and silt that are loosely cemented by calcium carbonate...
were used to help control the firing of the kilns.
In 1782, English potter and industrialist Josiah Wedgwood
Josiah Wedgwood
Josiah Wedgwood was an English potter, founder of the Wedgwood company, credited with the industrialization of the manufacture of pottery. A prominent abolitionist, Wedgwood is remembered for his "Am I Not A Man And A Brother?" anti-slavery medallion. He was a member of the Darwin–Wedgwood family...
created more accurately scaled pyrometric beads. This led him to be elected a fellow of the Royal Society
Royal Society
The Royal Society of London for Improving Natural Knowledge, known simply as the Royal Society, is a learned society for science, and is possibly the oldest such society in existence. Founded in November 1660, it was granted a Royal Charter by King Charles II as the "Royal Society of London"...
.
The modern form of the pyrometric cone was developed by the German ceramics technologist Hermann Seger and first used to control the firing of porcelain wares at the Königliche Porzellanmanufaktur (Royal Porcelain Works) in Berlin, in 1886. Seger cones are to this day made by a small number of companies and the term is often used in Europe as a synonym for pyrometric cones.
The Standard Pyrometric Cone Company was founded by Dr. Edward J. Orton, Jr. in 1896 to provide a calibrated, visual device to measure the amount of heat delivered to ceramic wares during firing. Following the death of Dr Orton in 1932, a charitable trust was established to ensure the continued operation of the company, for the benefit of the ceramic arts and industry.
Commercially produced pyrometric cones replaced glaze cones used by European and American potters in earlier times. Glaze cones were made by evaporating water from a liquid glaze until the resulting mass reached the consistency of a plastic clay. The plastic mixture was then formed into cones that were dried and set in a soft pad of clay in a kiln. When observed through the viewing port of a kiln the potter could see when a glaze cone had reached its melting point. Asian potters used draw rings, rings of clay dipped in glaze, for a similar purpose. The rings were removed from the kiln through special loopholes in the kiln walls using metal rods and examined for signs of melting in the glaze.
Ceramic Art
A biennial ceramic art exhibition for small work, The Orton Cone Box ShowOrton Cone Box Show
The Orton Cone Box Show is a biennial ceramic art exhibition for small work that started in Indiana, United States and is now held in Kansas, United States. It is open to submissions from across the world. The show's title is taken from the constraint on submissions, which must fit within the box...
, takes the Orton Cone company's pyrometric cone box as the size constraint for submissions.