Babs

Penetrating oil, liquids that dissolve corrosion/rust (e.g. LiquidWrench) can be helpful, again, depending.
Judiciously applied heat can be helpful, again, it depends!

Low fire clay remains porous even after firing. If the glaze has any crazing (crackling) in it, then the water can seep through the small cracks in the glaze and soak into the body.

I think we are overcomplicating this.
If glaze is fine then don't mess with the TC offset. If bisque is under-firing then either fire to one cone hotter if using the preprogrammed schedule or increase the final temp like Neil said. Given that ^07 is barely bending and you are aiming for ^06 then try firing to preprogrammed ^05. Approx 30C between 07 and 06 and 06 and 05.

That should have gotten you to cone 06, maybe even cone 05. It's really more important that it's firing accurately at glaze temps, which it is, so I wouldn't make any changes to the thermocouple offsets. I would just adjust the final temp up 30-40 degrees.

If everything completely dry, for a bisque, ware is not thick, you could set it at 100°C/hr to 600°C.
A photo of controller would help others give more helpful answers.
 

Ah our haptic seses are fully developed!
Keep in touch, be in the moment etc etc.
Good at shutting out the irrelevant when immmersed, apologies for cross references!

Monkey brains, you guys, no AI would calculate whete you are going @Hulk and @Dick White
Straight from glaze formulation to turbulent waters:-)))

Unlikely you will find one,imo. @Min gave the reason.
Chuck that bag of Gerstley out unless someone has the knowledge to identufy the substance it contains.
Get a check sheet going when you mix glazes, double check yourself...we've all, well I've had similar brain lapses or interruptions in the midst of making batches of glaze.
Tick substance, tick weight, tick into the bucket, that substance off the table.

I have had buckets of Mistake glazes, also Mystery glazes - bags of unknown origin that fired with desirable effects. Being the kind of potter who wants to make unique and original pieces, I cherish the special qualities and try to use those one-offs creatively while they last. The one-of-a-kind nature of That glaze on That pot can be a selling point.
Some of us older potters have experienced the disappearance of specific glaze materials and we don’t always try to replicate the lost effects, we just find what new stuff we can do with what’s available. There are so many possibilities ….

Perhaps if enougb of us we could get free testing!

Having recently worked at a pottery shop, where inexperienced young people mixed 10-20 gallons of glaze a day, I'll offer this: more than likely you carried over one of the percentages.
Rather than use 30% Spodumene you may have used 50%, for instance.
Considering the desired glaze is extremely matte I would suggest you added 20% Bentonite rather than 2%. 

Which controller do you have, the ramp soak - high limit, proportional or full blown atmospheric? Post a picture if you can. Shutting down at 1900 degrees indicates a safety of sorts. Either high limit or your pilot sensing dropped out. Since this happened twice at 1900 degrees it points to high limit, post your program.
Uneven reduction points to air leaking in which usually indicates the management of the atmosphere and the pressure in the kiln. Which can be damper operation, change in kiln power: gas pressure, burners, excess leakage, restricted flue…..
Natural gas should be very clean, (properly dirt trapped) and screens built into the the gas valve ought to catch any real small stuff. Cleaning orifices is fine, usually a spider web / dust. Normal recommendation would be NOT TO enlarge them even by a few thousandths so most often you will see a toothpick or soft copper wire suggested. Also ……… blow them out opposite of the gas flow. You need to remove the orifice to do this so the dirt is not blown back into the pipe only to return later stuck in the orifice.
If you have restricted orifices it’s usually obvious comparing one burner flame to the others, especially natural gas. Very blue flames are achievable. Not so much with propane.
BTW: it is common for gas kilns to be FULLY supervised throughout the firing. Set it and forget it more of an electric kiln thing. For gas check on it every 15 to 30 minutes seems to be the compromise to100% supervision.
 

Looks like #40 is more correct. Their new kilns are 240000 btu and …… my mistake #40 might be a bit large in the 6 burner so #50 gets you closer. Decent table here:http://www.davegardner.org/images/GasInfo/OrificeTable.pdf If you are lucky it is on the kiln tag.
Looks like you want to max out at 240,000 btu by todays standards which means #50 or slightly larger, closer to # 48. If you drill them yourself and don’t leave the conical approach in, they will not perform quite as well as if manufactured.  If you have #40’s in there and decent blue flame then I would definitely work the damper. Small (very small) adjustments will have very dramatic effects once you  get closer to reduction.  You. Want to keep as much heat in as practical, just short of reducing. This changes as the fire progresses and  as the operating pressure increases as well.
updrafts can be tricky (especially a small kiln) but folks have fired them for years so they can be mastered. It does take a reasonable amount of patience though. It would be great if you could watch someone fire successfully. When we do this usually folks observing see a few things that they never would have realized. Demonstrating the dramatic affect the damper has often enlightens may so maybe seeing is believing I guess.
zehat are you using as a damper?

I don't know who was selling type S for $50, but the ones I get from L&L were at least $150 at their lowest that I remember, about $250 two years ago, and are now $400. In addition to the thermocouple itself, you'll also need type S thermocouple wire all the way back to the controller. Also set your controller for type S. As to whether or not it will last, who knows? It all depends on the thickness of the wire in the sheath and the quality of the construction. Worth a try for $15, though.
The other solution to the flaking thermocouple is to install a ceramic protection tube. If you use a closed end tube you'll have to figure out what offset to program in the controller to compensate for the insulation factor (usually around 15 degrees), or you can get an open end tube that still keeps the flakes from getting in the kiln but doesn't require an offset.

There might be a shrinkage difference between the paper clay appendage and the already-bisqued hare. I would just make the appendage a bit bigger than the fired hare and fire separately. After firing, the paper clay bisque can be sanded down to fit and attached. Prepare both surfaces for the attachment as you’re making the new appendage. 

Ah our haptic seses are fully developed!
Keep in touch, be in the moment etc etc.
Good at shutting out the irrelevant when immmersed, apologies for cross references!

Ah our haptic seses are fully developed!
Keep in touch, be in the moment etc etc.
Good at shutting out the irrelevant when immmersed, apologies for cross references!

I agree, AI will not replace those of us who fully understand our particular niche, but that won't stop them from trying... until their reliance on AI dumps them someplace they don't know how to get out of, if only because they don't understand how they got in there. Sorta like the stories of a few years ago of people driving into swamps because that's what Google Maps told them to do.
And back to @Kelly in AK's unrelated question... Yup, about as unstable as can be. It's not a perfectly round cross-section, we do have a nearly imperceptible keel. The stabilizing force is the same as The Great Wallenda  - his long balance pole. Our oars stick out 9' on either side. As long as we keep our hands (on the oar handles) moving in the same plane parallel to the water, the oar shafts and blades will also form a line parallel to the water, and we don't flip. Deviate one inch with either hand, and it's all over. We have a semi-serious joke - there are 2 kinds of rowers: those who have been swimming and those who will be going swimming soon. (Yes, I have been swimming, several times.)

To round it back to AI, I think that all these personal experiences here about specific niches are why we aren’t in danger of being replaced. 

Monkey brains, you guys, no AI would calculate whete you are going @Hulk and @Dick White
Straight from glaze formulation to turbulent waters:-)))

Not pottery, but one of my other life distractions is rowing (in one of those Olympic-looking long, skinny, barely ass-wide boats with long oars). Someone in one of the rowing groups I hang out it asked an AI bot to describe how to achieve the optimal force curve during the rowing stroke. The bot went on for several paragraphs of blather, and ended with the suggestion you should talk to a knowledgeable person such as your coach.

Also there is a difference between glaze stains and body stains.

Invest in double sided sticky tape!
 
 
best,
Pres

For the help with the underglaze question. Now, does anyone have a source for an "anti gravity glaze or clay" so when I drop a form it wouldn't  hit the floor and break...........
Again thanks.
Graybeard
 
 
 
 

Also there is a difference between glaze stains and body stains.