Firing schedules for cone 07 and 8/9

[EmmaC]

Hi there!

I just bought my first kiln (Nabertherm) and have no experience in operating one before.  I am a bit worry about the firing schedule and wanted to know what are the best schedules for the cones I will be firing?

bisque firing - cone 07 , 980c

glaze firing - cone 9 (or 8?), 1280c

I do have a preset bisque firing schedule below  in the controller but it's only to cone 08.   what do you think of this schedule?  Will it be okay  if i just change the final temperature from 950c to 980? and if so,  should I change the hold time too?   

 

Thank you very much!!

[Bill Kielb]

This is an interesting question and we actually get it quite often.

A general answer for biscuit firing:

A schedule that burns out all the organics and ends at a cone that suits your clay and glaze application

• This firing will generally be to cone 04, 05, 06
• The firing must be long enough to effectively burnout everything and leave the clay in a suitable porous state for decorating and handling.
• Bisque firings generally take 8- 12 hours or more as time and time at temperature help burnout things completely
• Firing to a cone is a consistent way to measure heat work which is time and temperature so the use of witness cones is one of the only ways to consistently measure the heat work done.
• To approximate a cone with a controller, the last segment or last 100c should be fired at a certain rate to match the chart. 
• So in the chart below, to bisque to 05, (1036c from the center column reg cone) 1036 - 100 = 936c, the last segment starts at 936c, is set for 60c per hour and ends at 1036c for cone 05.
• Folks often find that bisque firing to 04 is needed to completely burnout all the organics in Their  clay which can reduce glaze issues later. (Cone 04 is higher in temperature than 05, 06, 07) and the “0” numbers are backwards meaning the smaller the number the hotter the firing so a bit counter intuitive.
• finally bisque firings usually go slower than glaze firings and generally do not exceed 100c per hour.

Orton cone chart https://www.ortonceramic.com/files/2676/File/orton-cone-chart-2016.pdf

For glazes and clay firing:

• Fire to maturity (cone temp of the clay) ensures strong least porous wares.
• Using cones as above as a guide will provide consistent insight into the heat work achieved to getting towards maturity
• Clay and glaze maturity should match so both are fired to their mature endpoints. Use cone 5 glaze for cone 5 clay.
• Generally glaze firings can be shorter (faster) 250 c per hour, so as little as 5 hours.
• To approximate the cone to fire to it should be done as above. Use the chart, subtract 100c from your final temperature and fire at the rate for that column as above. Again the center column, 60c per hour. For instance cone 5 would be 1186c - 100c = 1086c. Your final segment will be start at 1086, fire 60c per hour and end at 1186c.

Lastly, using witness cones is always a good practice so you know what cone you ended up with and - if you are going 60c per hour, there is really no need for a hold at the end. Everything will be firing evenly at that speed for most common pottery. Holds at the end can cause other issues and often cause the firing to move to the next higher temperature cone.

So to answer your question, a best schedule is the one that works best for your clay, your glazes and your application. General schedules are fine, but most folks refine their schedules over time to suit their products, practices, etc…. The basics still are the basics though so complete burnout and maturity are most often the goal.

Here is one of many you may want to read, available on the web and all about firing schedules: https://digitalfire.com/schedule/list

So to your schedule, it’s about 70c per hour for 8 hours, then 80c per hour for 4 hours, then mysteriously hold for another 20 minutes. It’s ok, likely gets to cone 06 / 05 / 04 by heatwork.

 

 

 

[neilestrick]

That's a bit of an odd schedule IMO. A hold time isn't usually needed in a bisque firing, and is only needed in glaze firings in certain situations. Here's a simple schedule I use for cone 04:

1- 65C/hr to 95C, hold as needed to make sure pieces are dry

2- 150C/hr to 963C

3- 60C/hr to 1063C

As Bill said, you can modify this as needed by changing the peak temp for whatever cone you're firing to, and reducing the temp for step 2 to 100C below that. You can also slow it down by reducing the rate in step to 125C/hr or whatever.

[EmmaC]

Thank you @Bill Kielb! This is super helpful for me as a newbie for owning a kiln!! I am going to save this down!

 

and thank you @neilestrick. i am going to modify your schedule and do a bisque fire to 980C. Thanks so much for sharing!