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As a newcomer to firing my own work can anyone explain cone tempretures? I have an electric kiln with a digital temperature control so i don't use cones.

So much advice refers to firing to cone 06 or 04... I've tried researching this but can't find a definitive answer. 

If kilns have advanced to accurate digital control why do i need cones and why can't firing advice refer to given tempretures? 

Any advice will be greatly received.

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Hi Denise. You might like to start with this little booklet produced by Orton, one of the manufacturers of pyrometric cones:

Cones and Firing (PDF)

The booklet will help you understand the purpose and mechanics of using cones (there's also a handy temp chart at the end of the booklet).

The 'advanced accurate digital control ' a kiln may possess is a bit one-dimensional; yes, it will tell you the absolute temperature a kiln has reached, but it won't tell you the amount of heat-work that the ware has undergone. In maturing glazes and clay bodies, that's what counts. It's a function of temperature over time, and that's what cones give an indication of.

It's also worth recounting that the only time I've known someone get into a really perilous position with their kiln (as in, life-threatening) was when they blindly accepted the display of their digital thermocouple, which unbeknownst to them had failed. On a gas kiln, which was on the point of collapse having over-fired by a considerable amount, and was quite literally melting. Truly terrifying,  and easily avoidable by having some cones as a back-up at least.

Edited by Sputty
Extraneous verbiage, AKA story of my life.
Rae Reich and D.M.Ernst like this

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Hi and welcome to the forums. 

Below is some background information that should be helpful.  One of the basic concepts to keep in mind is that cones measure "heat work" not temperature.  Heat work is the effect of heat over time and factors influencing heat work include final temperature, the rate at which the temperature increased, and time .  

 

Information from Orton on cones and controllers :

https://www.ortonceramic.com/files/2676/File/cones_and_controllers.pdf  

https://www.ortonceramic.com/files/2676/File/cones-and-firing-booklet.pdf (Also recommended by Sputty)

 

Here's a good post on factors influencing bisque "temperature"

 

-SD

Edited by S. Dean
clean up typos/formatting

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I always liken kiln-firing to baking. 

A cake is only cooked when it has been in the oven for a given amount of time, at a particular temperature. 

If you put a cake into the oven when cold, and let the oven warm to the required temperature, it would most likely be undercooked.  With our ovens, we can open the door and put the cake into a ready heated oven, and then leave it for an amount of time, until it is properly cooked. 

With our kilns, that isn't possible, so the cones tell us if our pots have been subjected to sufficient time and the required temperature. 

Clay requires "heat-work" - some heat for some time.

The digital components can fail (slowly) over time, so a perfect firing today, may not be so perfect in 20 or 50 firings time.  Use of cones will ensure consistent firing.

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denise, thank you for the question.  i had not seen the post above by Isculpt so i did not know i was, ( have been, am) considered "mean" oldlady.  my education has been by experience and learning from books.  i do not mean the single subject thin things that are so common today.  i mean textbooks with glossaries, cone charts and other useful information.   textbook seems to be a word nobody understands anymore in this world of phones glued to ears and videos of everything from how to hit a nail with a hammer to surgery.  if you watch one, you are an expert.

without looking at a cone chart, the reader of every word above this would not know that the cone numbers have a meaning that is not clear out of context.  the numbers that begin with zero, 022, 08, 06, 04  etc, read UPWARD IN TEMPERATURE.  cone 08 being cooler than cone 04.   once the chart reaches zero the numbers progress in temperature from cone 1 to a cone so hot that the spacecraft tiles are about the only thing made that hot.

now, someone with more knowledge will have something to criticize about this post.  go ahead, that is what a discussion is.  

Oh, yes, there is a book proclaiming to be the "bible" which has a cone chart that is mis-labeled.

Edited by oldlady
correct spelling
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The key thing is heat work. It is completely different than temperature. The kiln controller tries to estimate it by using temperature and time. But the only way to truly know is to confirm it using cones. That being said you don't need cones every firing. Once you know the kiln is firing to where you want it to be there isn't a real need to use cones again unless you want to check again, or your making changes to you firing schedule, or you suspect a problem is arising by noticing glaze differences/clay.

If your firing to cone 6. I recommend replacing the cone 5 with cone 5.5, Orton sells them. I emailed them asking some serious questions about the cone 5 cone. It made no sense to me how far away in temperature it was from cone 6. They agreed and informed me that is why they make a 5.5 cone. So if your going to order some get: 5.5, 6 and 7. This way you can accurately see where your at. 

 

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General purpose digital heating controllers used for industrial heating processes only look at temperature. But the digital kiln controllers built by Orton and Bartlett (and others), which are made to be used on kilns and have cone firing settings, do figure in heatwork. That's why we use them instead of inexpensive general purpose controllers. Are they as accurate as cones? No, but they are pretty darn close and with proper calibration they can be quite accurate, and are more than accurate enough for 99% of what potters do.

Digital electric kilns have a lot of fail safes, and are safer than the old manual kilns. Gas kilns are an entirely different beast, and should never be fired unattended IMO. Ultimately, you must be the one to make sure any type of kiln has shut off when it was supposed to. Manufacturers have told me that the electrical system in the kiln will fry out before the kiln bricks can melt down, but that doesn't mean you won't do considerable damage to your kiln before it gets to that point.

Do you need to use cones in every firing? That's up to you. I haven't used cones in my last 2500 firings. I don't see the point in having a digital controller if I still need to mess with cones. If the kiln under-fires, the cones will tell me by how much, but they won't prevent it. Same for over-firing (under-firing is much, much more common). I know my glazes well enough that I can tell if they're under-fired, and I keep up on kiln maintenance, so I don't usually have any problems.

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In addition to knowing the hot and cold spots in your kiln  (mostly if you have a single controller) I find cones are really beneficial when using a new kiln, changing firing program, after changing thermocouples or changing controllers. Once everything is calibrated then I find they are useful to use to verify firings, I don't put them in  every load. I also use them when doing a lot of glaze tests in a firing, I want to know fairly accurately what cone the glaze tests got to.

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I used cone packs in every firing when my kilns were new. Three per kiln load, bottom, middle, and top. Once I got to know how the kiln fires, and how to load it correctly, I found the digital controller alone to be very reliable. These days I only use cone packs right after I've changed the elements and thermocouples, just to make sure the new parts are working and I didn't screw anything up. If the cone packs in that first firing turn out as expected, I go back to relying on the controller. 

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Cones measure time and temperature (also called heatwork)

Since they are in kiln along with your pots they are the most accurate .

Controllers  recreate this electronically . These work really well but the downside is they can break but the risk is low as Neil says he has 2500 firings without cones.

They use thermocouples to get the info and these can wear out and can give false readings. Type S thermocouple are the most accurate and cost the most and last longer . Most kilns use type K thermocouples. I consider thermocouples to be the weak link.

In my temperature range and atmosphere (above cone 10 in gas reduction) these thermocouples are less accurate. I use platinum thermocouples which cost the most.

I suggest using some cones spread around your kiln and learn whats going on in all those locations before giving them up. Just as Mea says in above post.

Edited by Mark C.
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2 hours ago, neilestrick said:

But the digital kiln controllers built by Orton and Bartlett (and others), which are made to be used on kilns and have cone firing settings, do figure in heatwork. That's why we use them instead of inexpensive general purpose controllers.

 

I'm sure you're right. The behaviour of heat-work can be modelled like anything else, and that knowledge used to control systems, rather like a 'virtual' cone set.

But I have a feeling nagging away at me that distance is being placed between the potter and her work, another layer of abstraction which removes some of the immediacy and intuition of the craft. The first electric kiln I fired was controlled by simmerstats across three zones. Pretty much 'low', 'medium' and 'high'. You had little choice but to use cones, and spend time and thought in observation. You got to see glazes melt and heal over, you got to hold a rod through the spy-hole and see its reflection in the molten glaze. You had a connection, and you learned a huge amount by doing this. I simply don't believe that a singing, dancing digital controller can replace that.

There's a pottery not so very far away from me, the Poterie du Don. It's very well known, and rightly so, for its salt-glazed ware. Lovely stuff. But I remember some years ago reading about their new kiln - a computerised gas kiln, controllable to the nth degree - including the introduction of the salt! I was both in awe of the technology, and a little saddened by the 'progress'. My experience of salt firing is throwing packets of salt through the ports, drawing rings, observing and judging. I'm not convinced that pressing buttons in the right order can replace that intimacy, or the elation that comes when it all works as it should.

Just some musings, not to be taken too seriously. People have different needs, and different interests.

Edited by Sputty
I could go on for hours, so be grateful.
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