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How High Did I Fire?


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Firstly, let me say that I know this question probably can't be answered with any confidence, so I'm just looking for educated guesses.

 

I've attached a picture of two cone 4 cones from my last glaze firing (the first in a used kiln). Based on the results of the bisque (cone 08 flat at what should have been between 09 and 08 according to the controller), I knew that the temperatures displayed by the controller were less than the actual temperatures, but clearly under-estimated the difference at higher temps. 

 

I'm pretty sure I went over cone 5, since the cones are on their way to melting, but I'd like to know how close this looks to cone 6. Before anyone tells me I should have used 3 cones (3,4 and 5), I know. I had my reasons, which were probably not very good.

 

My kiln fired quite slowly towards the end of the firing - it took about an hour for the last 30 degrees C (54 degrees F), and the last 100 degrees C took about 2 and a quarter hours. I didn't soak at the end. So... if I reached cone 6 (or whatever), what was the max temperature?

 

I know I could look at the cones during the firing and work out how far off the thermocouple is that way, but I don't think it's worth getting welders glasses, so I'm just going to do this by trial and error, and hopefully a little help from you folks.

post-17614-0-56098400-1418762420_thumb.jpg

post-17614-0-56098400-1418762420_thumb.jpg

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I'm not going to crab at you because I have done these kinds of things too.

 

My guess would be about Cone 6. 

Since Cone firing is a combination of time and temp it is anyone's guess what temp you were at.

 

It would be cheaper and much less stressful to buy witness cones instead of firing by the seat of your pants time after time ...

but you know that already!! :rolleyes::rolleyes::D

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Yea you floored those cones and with the smaller one in there, i agree with CC. 

if you are using Orton cones , each size has a different melting temp.. i have a chart somewhere.. Ahhhh found it... 

 

 

 

 

Orton Pyrometric Cone Chart (Degrees Fahrenheit)

Cone Number

Self Supporting Cones

Normal Large Cones

Small Cones

022

1087

Not Available

1166

021

1112

Not Available

1189

020

1159

Not Available

1231

019

1252

1249

1333

018

1319

1314

1386

017

1360

1357

1443

016

1422

1416

1517

015

1456

1450

1549

014

1485

1485

1598

013

1539

1539

1616

012

1582

1576

1652

011

1607

1603

1679

010

1657

1648

1686

09

1688

1683

1751

08

1728

1728

1801

07

1789

1783

1846

06

1828

1823

1873

05 1/2

1859

1854

1909

05

1888

1886

1944

04

1945

1940

2008

03

1987

1987

2068

02

2016

2014

2098

01

2046

2043

2152

1

2079

2077

2163

2

2088

2088

2174

3

2106

2106

2185

4

2124

2120

2208

5

2167

2163

2230

5 1/2

2197

2194

Not Available

6

2232

2228

2291

7

2262

2259

1307

8

2280

2277

2372

9

2300

2295

2403

10

2345

2340

2426

11

2361

2359

2437

12

2383

2379

2471

13

2428

2410

Not Available

14

2489

2530

Not Available

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I would say 1-2 cones but I have never fired a cone further than 2 cones higher. I don't know what they tend to look like 3-5 cones over fired. Saying that my cone 8's look similar to that when I am firing to 9.5/10.

 

Maybe try taking half an hour off the firing time and see what cone/temp it gets to. 

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If your kiln took an hour for the last 50 degrees, that's pretty slow. I'd check to see if your elements are worn, of if your kiln isn't rated for cone 6. At that slow a rate of climb, the temperature for cone 4 will be quite a bit lower than the slowest (108F) rate of climb shown on cone charts. Cones measure heat work, which is dependent on the rate of climb. You've got to watch the cones bend to know for sure.

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(but I don't think it's worth getting welders glasses, so I'm just going to do this by trial and error)

it is worth it to by the protective eyeware-its not much$$ and you will need to view the cones to know anything about where the temps are as far as glaze work.You absolutely need to see the cones thru the spy ports.

Without the visual view of cones it will be all error.

Mark

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Pieter,

 

I really think if you go to your welding supplier you will find that the glass inserts used in welding helmets are very inexpensive.   Most welding suppliers also have a selection of  dark polycarbonate "sun glass" style safety glasses that welders and people that work near them use when not directly performing welding operations.  

I say this as long time member of ABANA  (Artist-Blacksmith's Association of North America)  One of the key safety issues for long term  Forge/Kiln/Glass  workers is the exposure to, not only ultraviolet radiation. but also long wave infrared radiation.  The damage that the eyes receive  from high temperature exposure is cumulative. 

 

I hope you have a lovely holiday and a safe New Year.

 

Lockley

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Pieter,

 

I really think if you go to your welding supplier you will find that the glass inserts used in welding helmets are very inexpensive.   Most welding suppliers also have a selection of  dark polycarbonate "sun glass" style safety glasses that welders and people that work near them use when not directly performing welding operations.  

I say this as long time member of ABANA  (Artist-Blacksmith's Association of North America)  One of the key safety issues for long term  Forge/Kiln/Glass  workers is the exposure to, not only ultraviolet radiation. but also long wave infrared radiation.  The damage that the eyes receive  from high temperature exposure is cumulative. 

 

I hope you have a lovely holiday and a safe New Year.

 

Lockley

 

 

I believe that Lockley is referring to something like this.  This design is made to go over prescription glasses and comes in shade 3.  There is another model which comes in shade 5 which offers more protection to your eyes.  However, I recall that many potter's find Shade 5 too dark.  

 

http://www.envirosafetyproducts.com/uvex-ambient-over-the-glass-safety-glasses-shade3-0.html

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Thanks for the info on glasses. They aren't as expensive as I imagined. However, my main reason for not getting glasses is that my kiln has a controller, so if I can adjust for the error in the temperature reading, I won't need to watch the cones during the firing. I don't think it's worth getting glasses just to figure out the error, and then fire with the controller from then on.

Of course, this is all assuming the error is consistent from firing to firing, but if it isn't, I need to get a new thermocouple. Actually, the controller is crappy in other ways, but that's a topic for later.

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If your controller is that far off, then either the thermocouple is worn, or there's something wrong with the calibration, or both. Are you programming it to fire to a specific temperature, or to a specific cone? If you're firing to a temperature, then you have to figure out what that temperature is for your desired cone as it relates to the rate of climb. If your controller kiln can't keep up with the programmed rate of climb, then you won't hit the desired cone at the programmed temperature. If you can't trust the kiln or controller, then watch the cones. Guesstimating will only give you more bad firings. A controller is no good if it doesn't give you the results. Plus, when you change the thermocouple in the future, you'll have to start all over with your estimates.

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It may help you to use the same size cones as well..   you will get better results , your Large cone is at 2120 F your small cone which is usually used in kiln sitters is 2208 F - I fire to cone 6 and 8 and always use a Large cone in the kiln to view and a small one in the sitter, when the small cone melts and trips the sitter off I know the heat work is done...

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I can program the rate of temperature increase, but above a certain point the kiln can't go more than 60 degrees C per hour, which is the rate at which I program the last 100 degrees to be fired at. I do this to be able to use Orton's cone chart to calculate the top temperature. When I decided on what temperature (on the controller) to fire to yesterday, I tried to take the slowing down into account, both in estimating the actual temp I reached the first time, assuming I fired to cone 5.5, and the actual temp I needed to fire to to hit cone 4. Whatever errors I made seem to have mostly cancelled out, as you can see by the cone pack.

I'm pretty sure the thermocouple is worn, and it's quite possible that it's never been replaced. It may also be that it was slightly damaged when it was moved. I will need to replace it at some point, but for now it looks like I can just adjust for the error. When I do replace it, it seems reasonable to expect that I won't have to do any adjustments to begin with. I plan to have cones in the kiln for every firing, so if the error gradually increases I can adjust for it accordingly.

I should add that it isn't essential for me to be that precise about what cone I fire to, since I'm not glazing my pots at the moment, and the only utilitarian things I make are planters.

Crusty, you're using the temperatures for a large cone fired at 108 degrees F per hour, and a small cone fired at 540 degrees F per hour. As I understand it, if they were fired at the same rate, they would bend at the same temperature.

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