First Glaze Firing Manual Kiln No Timer

[Christy Ann]

I bisque fired an old manual Paragon kiln for the first time, and it underfired slightly. Now I want to glaze fire these pieces at Cone 6 and could use some help in understanding what to do about the fact the bisc was slightly underfired, and I don't know what kind of firing schedule to use for Amoco Cone 6 glazes. The kiln has a cone sitter, 2 peepholes, and 3 dials (no timer or pyrometer). The dials can be set to low, medium, and high. Can anyone describe how low long I should keep each of the 3 dials at particular settings, and when I should remove each of the two peeps. This novice would be very, very grateful!

[Bill Kielb]

45 minutes ago, Christy Ann said:

I bisque fired an old manual Paragon kiln for the first time, and it underfired slightly.

How do you know it slightly underfired? It’s a manual kiln so 2 hours on low, 2 hours on medium, then high till end of firing and see if this gets you in the 5-8 hour range.

Edited January 11 by Bill Kielb

[Christy Ann]

I think it was underfired because I used witness cones and was firing to 06. The 06 witness cone did not go all the way down. The 06 cone in the kiln sitter did go down and turned off the kiln.

 

[Jeff Longtin]

Hello Christy Ann. 

Manual kiln sitters can be adjusted to match up with witness cones. It sounds like no one ever took the time to adjust your kiln sitter. There are several small screws that allow for the various moving parts to be adjusted. I won't offer advice until you post a picture of the actual kiln sitter.

Bill's advice about a standard firing schedule is a good starting point. The clay body you're using, and your making method, (throwing, hand building, casting) helps us give more accurate firing advice. 

[Bill Kielb]

3 hours ago, Christy Ann said:

I think it was underfired because I used witness cones and was firing to 06. The 06 witness cone did not go all the way down. The 06 cone in the kiln sitter did go down and turned off the kiln.

First before tweaking your sitter get a few firings under your belt especially with a kiln that’s filled. It sounds like it might be fairly close. If not and it’s just too far away, Sue McCleod has a decent how to on her website I believe. Orton cone photo below, notice the very small difference especially if the cone is not fully touching. At four o’clock we are only speaking of a degree or two. You may be just fine calibration wise.

Edited January 12 by Bill Kielb

[Hulk]

Looks like the image Bill posted correlates "o'clock position" to degree angle.

I'm not finding many graphics that depict correlation between degree angle and degree temperature.
This one is a large cone 10 cone; the rate* is indicated (in °C)

The temperature degrees per angle degree is greatest at the beginning of the fall/bend, least at the end.
More fun here: Untitled (thermaltechnologies.com.au)

How closely we have to hit the target for heat work for optimal results may certainly vary.
In my (limited) experience, within a half cone to a full cone is plenty close enough for bisque, given that it's not a full cone on the cold side, for then I have to rush a bit to keep the glaze layer from being too thick. I don't mind having to slow down a bit for bisque that's not as absorbent...
For glaze fire, some clays are much more sensitive to overfiring than others (per that same limited experience).
 

*Temperature difference between clock/angle positions depends on the rate - how fast/slow the temperature is rising.

 

Edited January 12 by Hulk
glaze dip "speed"

[Min]

@Christy Ann, like others have said underfiring a bisque isn't usually too big a deal but going forward if you use a "dirty" clay, like one of the dark brown bodies with lots of manganese or a red clay body, you might want to try bisque firing to cone 04. The extra bit of heat helps burn out more of the impurities as does doing a slower firing. (this helps avoid some glaze issues)

It's hard to tell how a cone 6 glaze firing is going to go based on a bisque firing. Being thoughtful about how you load the pots does help. As a general rule of thumb electric kilns will fire cooler at the top and bottom and hotter in the middle. To avoid underfiring top and bottom areas load less mass in these areas, this means taller pots therefore less shelves. If you have shallow / short pots load them in the middle of the kiln using more shelves.  

Some people like to watch cones towards the end of the firing. To do this you must use proper eye protection every time you look in the kiln. (like these ones) If your target is cone 6 then you would place 3 cones in front of the spyhole(s), cone 5 (sentinel cone) cone 6 (target cone) cone 7 (guard cone). Once you see cone 5 tip down then expect cone 6 to be down in very approximatley 20 minutes. (depends on element life and kiln size). Having the guard cone will let you know if you overfired and by how much. It can be very awkward to see cones so not everybody likes doing this, above all be careful if you do. Just need a quick look, don't sit in front of the kiln and watch them fall.

If your Amaco glazes have a recommended firing going to cone 6 then I would put the kiln on low for 2-3 hours, then medium for 2-3 hours then high until you reach cone 6. 

One thing that can make a difference in when the kiln sitter trips is how you place the cone in the sitter. If you find the kiln is underfiring (if only using the kiln sitter to shut off the kiln and not looking at the cone pack) then move the sitter cone over just a bit so the bar rests on the thinner side of the cone and the opposite for overfiring. Some people much prefer using sitter bars rather than cones so they are more consistent in how they bend and positioning doesn't matter.

Like Jeff mentioned it's also possible your sitter needs adjustment. Easy to do if that's the case, video here showing how to do so if you need it.

Edited January 12 by Min

[Christy Ann]

This is so incredibly helpful. I cannot thank you enough. I wasn't able to see the cones during the firing. I bought a pair of glasses afterward for infrared light and hope that helps. Your tips on going to 04 for dark clays, cone placement, and glaze firing timing are very helpful. Should I keep the peeps in or out during low, medium and high?

[neilestrick]

42 minutes ago, Christy Ann said:

Should I keep the peeps in or out during low, medium and high?

If you have a downdraft vent you need to keep all the peeps closed. If not, keep the top peep open for the entire firing.

[Kelly in AK]

Don’t place your cones too far from the peephole, they’ll get lost in the glow (advice). IR glasses were a great move for your long term eye health as well as to see through all the radiant energy.

I might put cone 7 in the sitter, then babysit the kiln till witness cone 6 goes down, shut off the kiln, then figure out how to adjust the sitter. I often have a misplaced sense of economy, so that’s not advice, more like a confession. 

[Bill Kielb]

7 hours ago, Christy Ann said:

Your tips on going to 04 for dark clays,

While hotter is better to some extent, bisque firings rely on time at elevated temperature. Most bisque firings are in the 10-12 hour range with a decent amount of time to 1000 degrees then probably a fair amount of time from 1500 to your cone. For a manual kiln it’s hard to hit specific temps so  mostly slow things down to last in the 12 hour range is always helpful whether cone 05 or cone 04 The time at the upper temperatures becomes important to completely burn out stubborn organics. Slower is generally more complete than faster. Not all clays need the extended burnout and some dark clay manufactures will provide a suggested schedule for their clay.

[Bill Kielb]

6 minutes ago, Kelly in AK said:

they’ll get lost in the glow (advice). IR glasses were a great move for your long term eye health as well as to see through all the radiant energy.

If all else fails, a cheap green laser pointer does wonders to cut through most atmosphere noise. Gotta wear IR eye protection though.