Converting From Celsius To Cones...

[Laragh]

Greetings!

 

I was wondering if any of you could offer advice/suggestions for me! I just moved to the US from Ireland. I studied Ceramics in NCAD in Dublin and I have just acquired my own studio in Raleigh and I'm working on getting it workable and liveable for August. Here I have noticed absolutely noone works in Fahreinheit... to explain what my issue is, I am fresh out of College and not only did I never work in Fahrenheit, I worked with two very very experienced technicians who never bothered with Cones..(They've worked there for over 30 years and are both accomplished sculptors)... I have been working in Clay for five years and I have no idea what a cone even is! For some reason I have a sense of shame and guilt about this even though I understand the atlantic ocean has created different ways of working!...Do you any of you have any reccomendations on a good article I can read to make sense of the changeover in my head? (Also so if someone is speaking to me about cones I don't just look at them blankly and say duhhhh...)

 

Thanks

[Guest Jessica Knapp]

Hi Laragh,

I'm sure others will have some suggestions for you, but to get you started, there's a Kiln Firing Chart available as a PDF on the Ceramic Arts Daily website's education section (http://ceramicartsdaily.org/education) that equates cones to the color in the kiln, and lets you know what happens at each stage. You're probably most familiar with the color in the kiln, and what is happening at specific temperatures, and this chart just adds the Fahrenheit equivalent and more column to the right, the cones that you use in each range. To find the chart, scroll down the page to the resources section, and click the link that says Kiln Firing Chart. The PDF should download to your computer immediately.

 

Typically you make a cone pack with at least three cones. One that is a cone lower than your target temperature, one that is the exact cone you wish to reach, and the last is a cone higher than your target. You can use more if you're trying to reduce your clay body at a specific temperature, etc. These three cones are placed according to the manufacturers directions into a long, thin pad of soft clay to stabilize them and keep them upright. This pack is allowed to dry before firing. Then, as you load the kiln, place the cone pack in front of a spy hole so that all three cones are visible.

When your target cone bends a certain amount, (depends on the glaze you're using, some people fire until the target cone--say cone 6, a common mid range cone for example--bends to 1 o'clock, 3 o'clock, touches the pad of clay, or is "flat" on the pad of clay the cone is embedded into) the firing is completed.

Cones don't equate to exact temperatures. Cones are manufactured so that they bend at different (and specific) temperature/ time combinations, dependent on the rate of temperature climb in the kiln combined with the actual temperature. In other words, they measure heatwork. For example, a cone might bend at a lower temperature in a kiln that is ramped up slowly, which allows heat to build and permeate everything inside the kiln. It may take a higher temperature to bend the cone if the kiln is fired at a quicker rate of degrees/hour, hence the open-ended nature of the temperature range/cone correlation shown on the chart.

 

You can also search for a cone chart from Orton, as most of the cones used in the US will be manufactured by that company. The Orton chart will give the approximate temperature/time combination at which each cone will bend.

 

Hope this helps.

Jessica

Greetings!

 

I was wondering if any of you could offer advice/suggestions for me! I just moved to the US from Ireland. I studied Ceramics in NCAD in Dublin and I have just acquired my own studio in Raleigh and I'm working on getting it workable and liveable for August. Here I have noticed absolutely noone works in Fahreinheit... to explain what my issue is, I am fresh out of College and not only did I never work in Fahrenheit, I worked with two very very experienced technicians who never bothered with Cones..(They've worked there for over 30 years and are both accomplished sculptors)... I have been working in Clay for five years and I have no idea what a cone even is! For some reason I have a sense of shame and guilt about this even though I understand the atlantic ocean has created different ways of working!...Do you any of you have any reccomendations on a good article I can read to make sense of the changeover in my head? (Also so if someone is speaking to me about cones I don't just look at them blankly and say duhhhh...)

 

Thanks

 

[Laragh]

Thanks Jessica!

That does help a lot I am still wondering though, why people use them? Everyone I know in Europe has never used them ! Any insight on that? I know they show you heat distribution etc ..but unless your kiln is on the fritz and inconsistent what is the need for them? Is it because people mostly use manual as opposed to digital here??

[Guest Jessica Knapp]

Hi Laragh, in my own work, I've found that I don't need to use cones. I fire mainly porcelain sculpture, mainly unglazed, or if I am glazing, I'm using a very stable glaze that works at cone 6-10. I'm not concerned with complete vitrification, water tightness, sanitary requirements or other issues that come up with functional work. I just ramp up using the same program to a specific temperature or if firing manual kilns, use only one cone in the sitter to shut it off at the peak temperature.

 

Some people use finicky glazes, and they've learned that the glaze matures when a cone is bent at a specific angle, much more accurate in some ways than a temperature reading. Others use cones because they fire in different kilns. Not all kilns (even digital computer kilns) measure the inside temperature accurately. The thermocouple may be older, etc. Cones, the small ones for kiln sitters, are also a fail safe of sorts, as they bend, they cause the kiln to shut off, saving a kiln from over firing with potentially disastrous results. The kiln may also fail during a firing, and cones can conceivably also let you know what temperature was achieved.

So, they're used for inconsistency in temperature readings, for finicky glazes and colorants that have a tendency to burn out if over fired, for those seeking consistent even temperatures across many firings for production ware, and for atmospheric firings like soda, salt and wood, which are typically all manual fired. I think in short the cones provide more, and more accurate information than the pyrometer.

[Laragh]

Interesting! Think I understand now..I also high fire

 

Thank you for your help, I am just out of college and have been mollycoddled by wonderful technicians for five years and setting up my own studio will be a trial..and probably quite funny ! Hehe

[hansen]

L: When Hermann Seger first developed the cone idea it was based on a constant ratio between in Unity between Calcium and Potassium of exactly 0.7 to 0.3 = 1.0 - then the ratio of alumina to silica kept at exactly 1:10 - okay? so then 0.7 Ca + 0.3 Na + .03 Alumina + 3.0 Silica when fritted and manufactured into a cone melted at cone 3. See? Look at the numbers for Alumina and Silica in the example. While keeping the Ca & Na equalling 1.0 if you insted used 0.5 alumina and 5.0 silica = cone 5. 0.9 alumina + 9.0 silica = cone 9

 

Although Orton uses slightly different proportions, the idea is still the same. Cone is an expression in Unity of chemical ratios. It has nothing to do with temperature. The point of deformation of the cone of course, becomes possible through advancing temperature, but time is a factor as well. For example, in old China the temperature reached was never beyond what a 12 hour firing to cone 6 would reach, but they fired for 10 days to cone 10-11.

 

Reaching 1300 degrees and holding for one hour is very different than holding 1300 degrees for 12 hours, for example.

 

In the days of programmable controllers we have now begun to use temperature instead of cone. We use our kilns more like ovens when actually they are a bit like welding torches - you want your material to reach the proper melting points so you have to factor both time and temperature; this is called "heat-work" - additionally, the thermal mass of the wares, hot face, and kiln settings and furniture plays a part in defining the ramp of the kiln both up and down.

 

It is an interesting study in and of itself, I would never call it irrelevant if you want to be proficient and well-informed as to ceramics techniques. Orton has a CD you can ask for too, probably free. Do a google search and see what resources are available. At certain time & temperature points, say a kiln increasing at 100 degrees and hour, there is an estimation of what cone you are at. This is different in a kiln increasing at 300 degrees an hour, so Orton has plotted a chart.

 

Archeological analysis can tell us what is in a glaze or clay, the ultimate percentage analysis or UPA, whach can be converted into Unity; and to what temperature it has been fired. Archeology can tell us what the kiln was constructed like. What it cannot tell us is cone - not yet anyway

 

h a n s e n

 

p.s. kilns rely on cheap pyrometers which are exposed to the heat so they will gradually give a different reading especially when they are going bad. Some pyrometers are better than others. The best measured light waves however, and are usually highly accurate over time. Expensive however.

 

 

 

 

Thanks Jessica!

That does help a lot I am still wondering though, why people use them? Everyone I know in Europe has never used them ! Any insight on that? I know they show you heat distribution etc ..but unless your kiln is on the fritz and inconsistent what is the need for them? Is it because people mostly use manual as opposed to digital here??

 

 

 

 

[Marcia Selsor]

Thanks Jessica!

That does help a lot I am still wondering though, why people use them? Everyone I know in Europe has never used them ! Any insight on that? I know they show you heat distribution etc ..but unless your kiln is on the fritz and inconsistent what is the need for them? Is it because people mostly use manual as opposed to digital here??

 

 

I was just about to send you the same site for the cone chart that Jessica sent. Temperature cones have been around since the Northern Song Dynasty. Wedgewood made his own. Orton made them beginning 1896. <- from Wikipedia. More people have gone digital in the last decade or so. For wood or soda firing, digital pyrometers could be damaged. Maybe old habits die hard. According to ethnoarcheologists, pottery communities and fishing communities hold on to their traditions more than any other. You are of a younger generation who grew up with digital pyrometers. It is the norm for you. It is recommended by many to use 'witness' cones in the kiln with the digital controls. It may just be old-fashion.