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Understanding creep behavior provides insights for design improvements and quality assurance.
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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!