Cones and timing

[Wingnut]

Hey Everyone,  I'm so glad I found this forum.  Been reading it for days now.  Simple question here as I'm still figuring out my new to me 1985 (in good  condition) small Cress kiln.  Last evening's bisque firing was my 2nd attempt at low temp firing.  I know what happened to first after call to Cress.  Now for my 2nd attempt at bisquing: Timer set for 6 hours, speed control on E.  The 04 cone in the kilnsitter did its job and bent (kiln turned off itself)  The 04 witness cone did not bend.  However, the witness cone is  smaller and darker red. The greenware looks like it should after firing.  Next time, I'll put an 04, 05 and 06 witness cone in to better gauge the true temp.  And set time for 7 hours.  My question is: if the 04 kilnsitter cone bent, why didn't the witness cone.  Should I have continued to manually fire until witness cone bent? Any advise or thoughts is appreciated. 

Thanks,

Jane

[Bill Kielb]

The cone sitter can be calibrated so there is that but your witness cone location, kiln loading  and firing speed etc.... can have an effect. You mentioned this was a bisque firing, most bisque firings take much more time to ensure all the organics are burned out. Time is often an essential component and slower firings most often will result in more even firings. I don’t believe I have seen a typical bisque firing to 04 go faster than 10 hours so this could explain the difference in cone bend.

having said all that I agree that using the guide, firing, guard cone  pack helps to determine exactly what it fired to and from there you can  tune your firings and kiln as well. Kilns are not always evenly heated as well so often the bottom is cooler, but I have seen the middle cooler due to element location and top as well due to lid losses.

google the Bartlett genesis controller and look at some of their cone fire schedules to get an idea of some conventional firing schedule speeds.

and lastly cones will bend at their prescribed temperature if the last 200 degrees of the firing are fired at approximately 108 degrees per hour for today’s typical cone chart. This is where the majority of the heatwork is done and for glaze firings is very important. Think of it as cooking a pizza, you could try forever at 150 degrees but it likely will never cook but 12 minutes at 375 and you have a masterpiece. The last 200 degrees of the firing is where glazes experience the most relevant heat-work. 

Cones are made of glaze and generally fully melt 6 cones higher than their rating. They soften enough to bend at their value so they are a good indicator of heatwork. A cone rated at cone 4 will  fully melt into a glaze at cone 10.

[Mark C.]

The sitter cone bent at cone 04-cone bars are more acurate for sitter use than tapered small cones.

The sitter has some adjustments(google dawson cone sitter adjustments)You can make adjustments to some smaller degrees at the sitter-but also you can use a higher cone bar to up the temps in rest of kiln for a glaze fire. testing is key

The larger visual witness cone is whats happining on thet shelve at that spot.-this is where the pots are and for a Glaze fire you want the witness cones to be the ones that melt right.

In a bisque fire its not so important.

You need more witness cones all over the kiln in your glaze fire to see what the temps really are-it will take three witness cones per location (all different temps like 04-05-06 asuming your best temp is going to be 05) to know whats happening where.

Use the temp cone you want to end at to be the middle cone in the witness cone packs.

[Wingnut]

Thanks for sharing.  This info seems like it will be very useful as I get more into this new hobby.  So much to learn.  I am thinking I'll stick with 04 bisquing and 06 glazing until i master it.