Bill Kielb

Stulls graph does not show melting point in cones

I am thinking the confusion arises from the lack of explanation of cones. While their chemistry is established they indicate by bending so not really fully melted. A cone 4 cone ground up and fired to cone 8-10 turns out to be a fully melted glaze. At present there is not a straightforward exact predictor of when a composition will fully melt. Stull did his work at cone 10 I believe (likely closer to cone 11 today). His map was for a very specific flux ratio and his glazes. Katz showed a reasonable correlation at cone 6 and lower further incorporated boron as a means to lowering the melting temperature. Sue McCleod presented a cone six version of this at a2018 NCECA (Google Sue McCleod and Stull. Stulls map does not predict the temperature something melts at. Higher melting temperatures would progress from left to right and upward in relative ranges. Limits are these tested ranges, but are approximate guidance Testing is generally the only way to know with reasonable certainty when something will fully melt. Advanced knowledge of durability is a Katz thing where certain flux ratios may be an indication of durability. I think the simple answer is cones fully melt 4-5 cones higher than their rating. I don’t think the author clearly represented this in the cited link. I would also suggest that much of pottery is understanding the variability and by experience important trends. It is somewhat very exact and scientific but verified through testing.

Looks like a small well powered kiln. Depending on reduction schedule and firing speed restrictions of the wares you will fire likely 8 - 10 hours. If your wares are not particularly thick and you can go 400 - 600 degrees per hour with let’s say a 45 minute early reduction maybe gets you a bit faster down to 6 hours. This kiln looks like it can go to cone 10. One thing about small updraft kilns folks are prone to stalling them in very heavy reduction. The supervision of damper and gas is often something to get used to and too heavy a reduction will drop your speed a bunch. In my experience most folks tend to stall these kilns on their way to cone 10 so cone 6 reduction should be easier to hit.

It’s pretty easy to do by hand and if you are proficient with excel, there are some spreadsheets that relate it well. Regardless, knowing the concept then comparing glazes under UMF evens the playing field so to speak so one does not have to learn it to use it productively. The comparisons have more meaning and trends are more easily recognized under UMF.

Sounds like you figured out gas / damper and reduction indicators for you so your heating rates are acceptable. I have never had to strike or go into heavy reduction at the end but if you get the result you are looking for, then it is a technique successful for you. There are many schedules and techniques, I have never had to strike nor clean up the kiln at the end. My goal is always to get the uniform reduction I am seeking without a smokey mess and waste of fuel. Some test tile pics and midfire / later fire flames below. I use an O2 probe and built monitoring equipment, so a bit unfair, but a way to learn / teach basic reduction. What works best for you and your glazes you will figure out - have fun firing!

Nope, temperature and apportionment change. Under UMF fluxes add up to one by definition- always. So Glaze calculating software sums the fluxes to equal one and everything else is apportioned accordingly. The fluxes traditionally have been Lio2, K20, MgO, CaO, SrO, BaO, ZnO. Alkaline metals and Alkaline earths respectively. You end up with a consistent way to compare glass former's, stabilizers, and even ratios that become meaningful with testing. Setting fluxes equal to one (unity) is a requirement to place things in UMF form

If your electric shuts off at the fuse box that indicates a short or over current condition. You will need to have someone troubleshoot and find the shorted connection. If your firings have been taking longer that would indicate your elements are wearing out. When elements wear out their resistance value increases and your kiln actually draws less current which means less power to fire. You may have both problems but the short circuit that is tripping your breaker is the one to find first and fix. From there have your electrician measure the resistance of your elements and if they have risen from new by about 10%, they are ready for replacement. A thermocouple would not cause this to short and trip the main breaker.

They sort of all follow that once gravity takes over they bend quickly within just a few degrees. From three o’clock on things happen pretty quickly

Some folks use underglaze on greenware, some folks underglaze on bisque. Some folks underglaze one coat on bisque, bisque fire again and add more underglaze to their design without fear of disturbing their first coat. So on greenware, I guess it’s fired only once if it’s fired from green to glaze as a single fire. If it’s applied over bisque then it still only goes through a single firing - the glaze firing. If an extra bisque firing is done for multiple coats, then the first coat of underglaze is fired more than once counting the glaze firing. So the extra firing allows one to decorate over an already underglaze decorated design.

I would say a strong six or barely over six, almost darned near perfect. Maybe a degree or two or an extra minute or two. I would be pretty happy if my kiln fired that way all the time for that matter. You can do a small cone offset to get it to your liking, but I would do that based on a reasonably filled kiln, probably not a mostly empty one. Just wondering if the cone was damaged at the base before firing?

Did the kiln turn off because it reached your firing cone? If it reached cone then even propped open slightly your firing ought to be near normal. What is your firing schedule, what is your target cone, what cone are your clay and glaze, what turned the kiln off?

This looks like one of those miracle clays but is really a cone 9/10 clay to get full verification. So it ought not bloat at cone 6/7. Can you post a picture or pictures of the defects you are seeing?

Likely need thin the glaze to spray. Dry the glaze as needed with half pull of the spray gun trigger - air only - should make spraying more doable. It’s good practice to learn the thickness with some test tape when spraying with glaze, since it’s thin to work in the sprayer it will go on very even, but thinner than dipping. Usually requires several even coats dryed in between by “air only“ from the sprayer. Don’t forget proper mask and ventilation!

Yes, updraft, downdraft powered and atmospheric it’s a dance with gas pressure and damper. Damper adjustments are often tiny. I have seen 1/16 inch have the effect of decent reduction or smothered not able to gain temperature. Firing with someone who is good at it would help a whole bunch. It’s always been better when I was personally there as opposed to digitally there on teams or FaceTime etc… Truly best if someone can show you IMO.

In the US minimum clear space is usually 10’ (3.048m) minimum. This will be dependent on local codes for your location. My thought: if they can relatively easily extend it farther regardless of the code, they may just want to do it voluntarily.