A good Cone 5 firing schedule

[Michael Huang]

Hi all, 

I'm in search for a good cone 5 firing schedule that create the least amount of defect, 

we are firing a new skutt kiln KMT1027-3, 

they use to firing on preprogram cone 5 schedule and are running into defects problems like pinhole and blisters.

I search around the wed and come up with this schedule,

 step    °F/hr / F    Hold
1    200/180    60
2    200/1100    0
3    350/2053    5
4    100/2153    0
5    9999/2053    30

but still seeing pinhole on some glaze,

is it the glazing issues, or a firing issues?

I would love to hear from you guys. 

[neilestrick]

No need for a hold in the first segment. Explosions aren't a concern with glazed pots unless you just dipped them and put them directly into the kiln and are firing very fast.

Segment 2 is unnecessarily slow for a glaze firing. Get rid of segment 2 and go 350/hr after segment 1.

Segment 3 should go up to 1953. Run the last 200 degrees at 108/hr to 2167.

Did the preprogrammed setting work in the past? There's no reason it should suddenly stop working unless something is out of whack. Have you checked the condition of the thermocouple? Have you put cones in the kiln to confirm that it's firing accurately?

 

[Bill Kielb]

I agree with Neil, that schedule seams a bit random. For the pinholes you may have success by finding a best drop and hold that heals your most difficult glaze.  Did you achieve cone 5 with a witness cone? Pictures of the defects might help here and am also curious if the cone fire schedule for cone 5 does not work as well.

[Michael Huang]

19 hours ago, neilestrick said:

No need for a hold in the first segment. Explosions aren't a concern with glazed pots unless you just dipped them and put them directly into the kiln and are firing very fast.

Segment 2 is unnecessarily slow for a glaze firing. Get rid of segment 2 and go 350/hr after segment 1.

Segment 3 should go up to 1953. Run the last 200 degrees at 108/hr to 2167.

Did the preprogrammed setting work in the past? There's no reason it should suddenly stop working unless something is out of whack. Have you checked the condition of the thermocouple? Have you put cones in the kiln to confirm that it's firing accurately?

 

the reason I run the first segments is because the studio I'm in right now are full of students and new members, 

all on different levels, also not sure how long their pieces been sitting there.  

the preprogramed didn't work too well, lot of the pieces come out with defects. 

the witness cone on top and bottom shelves are band but didn't seem like it hit cone 5, 

and middle is drop to the point the tip is touching the shelf. 

I don't have photos right now, 

but I'll add them when I have it. 

[neilestrick]

9 minutes ago, Michael Huang said:

the reason I run the first segments is because the studio I'm in right now are full of students and new members, 

all on different levels, also not sure how long their pieces been sitting there.  

For a bisque firing that's good practice. But if they've already survived bisque then they're going to be fine in the glaze.

The middle likes to run hotter than the top and bottom in Skutt kilns. Load the bottom looser, or with pieces of low mass like bowls. Put tall stuff at the bottom, too. Load the middle tight, with small pieces and flat pieces that require a lot of shelves. Lot of dense mass there. Load the top similar to the bottom, with lower mass pieces.

[Min]

Are the pinholes and blisters on pieces in the cooler parts of the kiln? Are the claybodies okay as far as absorption for functional pots like vases and mugs at cone 5? 

[Morgan]

Big fan of a drop and hold/soak for healing pinholes and blisters. I use the natural cool digital fire one but you could easily alter it for cone 5.

https://digitalfire.com/schedule/plc6ds

[Michael Huang]

Here is the witness cones. 

and below is the schedule 

1	200/350	0
2	350/1100	0
3	350/1953	5
4	108/2167	0
5	9999/2053	30

 

we are still running in to pinhole problem, but isn't as bad as before. 

 

packing the top and bottom light, and middle heavy.

for my understanding our kiln still run too hot. 

not sure how to fix that. 

should I try firing to cone 4 and hold to cone 5?

 

Untitled document.pdf

[Bill Kielb]

Cones are reasonably close, tcouple offsets likely get you a bit more even.  Lots of possibilities for pinholes but there is a good chance they heal with drop and hold since you mentioned it is an improvement over a standard schedule drop and hold seems to be the likely best approach..  Experimenting with the drop and hold time will take some effort and testing though. You are looking to drop the kiln to a best temperature for the troublesome glaze to begin healing then hold for sufficient time to heal all pinholes. You are doing this blindly and inferring results from various fired results and  an orderly change in settings.

Just curious, what is the five minute hold for?

Edited June 22, 2022 by Bill Kielb

[Hulk]

A few degrees less for the peak temp, then a controlled cool to about 1850F after your thirty minute hold might help (and then would be close to what I'm doing, which started out to clear bubbles/fizzing). I am holding at 100F below peak for longer, closer to forty-five minutes to an hour.