Bill Kielb

I have a small gas kiln (8 cu. ft) made from fiber board. Two layers of 1” board. Has no problem getting to cone 6. It was cheap and easy to build but I won’t  build another. I agree with the points @neilestrick made and have a couple more. Fiber board has its strengths, being rigid and super insulating, but it has some drawbacks. One is that it will shrink. Once you fire your kiln (unless you pre-fire the boards) you’ll have to re-fit it because big gaps will form. The other is that it’s really friable. As bad as fiber blanket, in my opinion. Even though it’s rigid it’s not strong. Every time you lift the lid or open the door, you’ll be abrading it. The wear and tear is one thing, all the respirable silica it releases is another. 

Your best bet is to talk to a refractories supplier. They'll be able to recommend the best product for your application. There are a lot of different types of insulating fiberboard out there. Regardless of the type, though, how do you plan to mount the elements to the inside walls of the kiln? IFB will probably be the cheapest, easiest and most durable way to build it, and it's clearly insulated well enough if you get to cone 6 in 3 hours. Why change the design?
14 amps x 120 volts = 1680 watts. 

Fairly high boron levels in both, but especially the second recipe. Holding boron constant might be a good thing here.

Not sure. The Katz and Carty research indicates boron requirements are fairly linear and predictable. I mention because 0.43 BO approaches the requirements to melt a glaze at 04. I am not aware if the data are flux specific though. Interesting !
https://ceramicartsnetwork.org/docs/default-source/uploadedfiles/wp-content/uploads/2008/10/tf-boroninglazes-0912.pdf

You have it right, the manufacture has it right, the inspector has it wrong. Interestingly a 60 amp breaker is the minimum allowed. Breakers that you buy for home are usually rated and thermally limited in load to no more than 80%. 80% of 60 amps is 48 amps. Lots of folks know the 80% rule so if it dawns on him he may suddenly change his mind. In the end your electrician has it right and can point him to the NEC and NFPA requirements for a continuous load - resistance heat. Basically not less than 125% nor greater than 150%.

In my experience
Likely no worries as long as the controller will resume the new program. Until you get within the last 200 - 300f degrees of your cone in theory not much of the final melting work has been done so  everything should be fairly reversible.

Switching elements is a thing, but this kiln already was designed and calculated using uniform graded elements. Besides, the voltage drop produces unwanted heating wherever it is occurring (wire, connections, sub panel, breaker ….) which then becomes a fire hazard. Find and fix the issue first and foremost. Applying load changing techniques will actually increase the heating in the defective areas (wire, breaker, sub panel …) for which they are likely not designed or rated. So really a last resort that requires verification for entire system safety appropriately and then this kiln cannot suddenly be used at its standard rated voltage so marking appropriately. I would suggest It’s really something that can only be done by those appropriately skilled in doing so as it can increase the risk of fire in the whole system without appropriate precaution and verification.

It was a safety thing -- it (understandably!) didn't like the debris in the valves.
Unpacked the kiln this morning -- beautiful firing and in the shortest firing timeframe reflecting the original manual. So happy a potter all round!

Just some personal observations
It’s gonna be tough but for large drips and by hand something pretty course may help so 60 - 80 grit likely best to remove significant drips or get them to a point where they can be polished. For polishing all my feet I use 12” 180 grit or higher glued to a batt. My wares are porcelain and have trimmed feet so super smooth is my typical finish.
There is no rule to dipping other than learn by test tile how a glaze responds to your dipping practice. I dip for three seconds, other may dip for longer.  I always make test tiles using one dip, two dips etc…. For each test.
Grogged clay often becomes rough when the grog is exposed during wet finishing. The only way I have been able to get them smoother is to sand after bisque (appropriate dust mask and practices required) using 220 grit paper. As the clay shrinks the grog can poke through so finishing before bisque can raise the grog actually. It’s one of the reasons I pretty much only throw porcelain now.

So the kiln has manual controls, you're just looking for a pyrometer to track the temp as you fire, correct? Any type K pyrometer will work. The beefier the thermocouple the better, so don't get one of those off Amazon that has a very thin thermocouple. Look for the type that has a ceramic block that holds the thermocouple. There are several on Amazon that will work, or any of THESE on Clay-King.com are good options. Even the cheap ones work well, I've tried out several of them. You can either drill a hole through the kiln body for the thermocouple, or stick it in a spy hole and pack some fiber around it.

@Bill Kielb Thanks for the response. 60-80 grit for big drips and 180+ for finishing bottoms sounds about right. It's really unfortunate that my favorite results tended to be the glazes that got the most movement, but at least it was a mostly successful experiment! As for my dips they are pretty quick in general, definitely 3 seconds or less if I'm going to layer. I didn't mix these particular glazes (they are older recipes from the craft center that I tech at) and they don't have any gravity documentation. It's mostly a go by feel studio so my mileage with technique is going to be varied for the next month unless I take over some of the glaze mixing : /. I'll be honest, I seriously considered trading in this dark groggy clay for a white grogless stoneware because of all the struggle it imparts on making work (best thrown soft, but don't use a lot of throwing water, if you trim you gotta burnish, if your walls aren't just right you'll get some bloat, all your standard glazes get an iron oxide shower, half the glazes wanna crawl, rough bottoms, many people don't like texture, etc etc etc). But after a few days I'm back to looking for solutions! Anyway, thanks again for the response.

Just some personal observations
It’s gonna be tough but for large drips and by hand something pretty course may help so 60 - 80 grit likely best to remove significant drips or get them to a point where they can be polished. For polishing all my feet I use 12” 180 grit or higher glued to a batt. My wares are porcelain and have trimmed feet so super smooth is my typical finish.
There is no rule to dipping other than learn by test tile how a glaze responds to your dipping practice. I dip for three seconds, other may dip for longer.  I always make test tiles using one dip, two dips etc…. For each test.
Grogged clay often becomes rough when the grog is exposed during wet finishing. The only way I have been able to get them smoother is to sand after bisque (appropriate dust mask and practices required) using 220 grit paper. As the clay shrinks the grog can poke through so finishing before bisque can raise the grog actually. It’s one of the reasons I pretty much only throw porcelain now.

Just some personal observations
It’s gonna be tough but for large drips and by hand something pretty course may help so 60 - 80 grit likely best to remove significant drips or get them to a point where they can be polished. For polishing all my feet I use 12” 180 grit or higher glued to a batt. My wares are porcelain and have trimmed feet so super smooth is my typical finish.
There is no rule to dipping other than learn by test tile how a glaze responds to your dipping practice. I dip for three seconds, other may dip for longer.  I always make test tiles using one dip, two dips etc…. For each test.
Grogged clay often becomes rough when the grog is exposed during wet finishing. The only way I have been able to get them smoother is to sand after bisque (appropriate dust mask and practices required) using 220 grit paper. As the clay shrinks the grog can poke through so finishing before bisque can raise the grog actually. It’s one of the reasons I pretty much only throw porcelain now.

@Rpsa just to add here stroke and  coat glazes generally melt at cone 04 (low fire) but seem to work well at higher cones as well. They are opaque, but that’s not to say an 04 clear glaze would not work fine over underglaze. While experimenting, I found I could make a glaze act like stroke and coat by having enough boron to melt at 04 but enough alumina so it would be a stiff glaze that traditionally does not run. These glazes would melt fine at 04 and tolerated firing well beyond that temperature. Is this how they make stroke and coat, I don’t really know. I mention because if stroke and coat has a clear version, then I think it likely would work fine.

I have not had great results refiring to cone, nor do I think underglaze will act as a decent primer, but ya never know what the result will be till you try. To drastically change the look, I have fired down  over an existing glaze and had reasonable success with lowfire glaze though (similar to some production wares that go to cone first to weed out potential failures in advance) so maybe an idea that is worth mentioning. Heating the ware and spraying the final glaze made even application very doable.

Hi and welcome to the forum!
What I’m really finding in my own testing is that colourants have a much stronger affect on the possible durability of the end result than is often assumed. I had a similar experience where a base glaze has pretty good numbers on paper, but certain unexpected colourant additions made some tiles fail a vinegar test (iron!?). My flux ratios and silica balance are similar to what you have listed, and I’m currently running some line blends to see if I can keep the same colour response while increasing the silica for durability. 
Dishwasher tabs do contain a lot of alkaline chemicals, including sodium carbonate (soda ash), that will etch all dish ware over time, not just pottery. It dissolves the silica. So testing ware in a way for dishwasher durability in a short amount of time that isn’t also too heavy handed is tricky, I think. I think the digitalfire recommendations that it looks like you followed may be too harsh.
 I’m going to tag @Minbecause I think she had different recommendations about the concentration of the soda ash solution, but I can’t remember the numbers she used. 
 
 

Hi Marie and welcome to the forum!
My experience with the 5% soda ash test when testing the black glaze Licorice from the book Mastering Cones 6 Glazes by Hesselberth and  Roy  led to a degradation of the glaze gloss level. I then went on to leave a test piece in the dishwasher for several months. Real world dishwasher tested did not show any degradation. I do think the soda ash test is too harsh a measure. Note it is within a hair from the "ideal" flux ratio. I did contact Roy about this and he didn't recall doing the soda ash test with this glaze.
If your glaze can take it increasing the silica and alumina in a formula will improve durability  regardless of flux ratios.
Regarding the "ideal" flux ratio of R2O: RO of 0.30:0.70, have a read of this snippet from Matt Katz's 2016 article Glossed Over: Durable Glazes from NCECA 2016
note the test for this article with a 0.1:0.9 ratio was "surprisingly robust" and the need for further research regarding the effects of silica:alumina ratio and the use of colourants. I don't think we are at an absolute conclusion yet in regards to flux ratios. They do not stand alone insofar as durability measures.

One more tidbit, I’ve had glazes crawl that otherwise don’t when I stick them in the kiln right after glazing and fire it up. These would be glazes that are bought premixed dry, so I haven’t a clue to the formulas. Applied too thick (usually) and/or fired too soon after application, they’re candidates for crawling. Student work, the defect is fixed by counseling on glaze application and time management. 

Here's a revised Spearmint recipe that I use in my studio, and I've never had problems with it:
Gerstley Borate   11.5 Frit 3134                  5.53 Neph Sye                  4.27 Whiting                  17.58 Calcined Kaolin    8.22 EPK                           22.38 Flint                          30.53  
 
Spearmint.pdf

@s6x I think the ideas above very helpful, just need to add: Vent a kiln likely a must in your basement capable to remove the kiln off gasses and the heat produced by it.  Along with that the vent will need to be able to draw in its own outdoor air for cooling. Since you have a furnace (and likely a dryer) you will need to make sure the vent can be supplied it’s own air and not pulled back through an appliance such as your furnace or dryer.
when in doubt, since this is your home rated fire protection material is important. Type X 5/8” drywall has a fire rating. Drywall works as an approved rated fire barrier because the moisture bound in it is an important component of the protection. Cement board is great for its sturdy structure, but generally is not a rated fire barrier material. You are trying to protect the combustible materials of your home.
So not undoable, but well thought out ventilation and protection with sensible operation to remove all excess heat throughout the firing worthwhile IMO.
 

Took the panel off, found a wire on the 3rd element to the switch not connected good, fixed that. Also the top element was broken where it bends in through the brick. I guess my moving was kinda rough.  Going to order all new elements and see what gives, lol.

@s6x I think the ideas above very helpful, just need to add: Vent a kiln likely a must in your basement capable to remove the kiln off gasses and the heat produced by it.  Along with that the vent will need to be able to draw in its own outdoor air for cooling. Since you have a furnace (and likely a dryer) you will need to make sure the vent can be supplied it’s own air and not pulled back through an appliance such as your furnace or dryer.
when in doubt, since this is your home rated fire protection material is important. Type X 5/8” drywall has a fire rating. Drywall works as an approved rated fire barrier because the moisture bound in it is an important component of the protection. Cement board is great for its sturdy structure, but generally is not a rated fire barrier material. You are trying to protect the combustible materials of your home.
So not undoable, but well thought out ventilation and protection with sensible operation to remove all excess heat throughout the firing worthwhile IMO.
 

I routinely do both, however easiest to bisque fire the underglaze for the ease of handeling while completing the decoration. I spray most of my glazes so really this poses less of a concern. What I have found, regardless of the application the underglaze and overglaze really need to be tested together. Some combinations shift color, some overglaze has a bit of difficulty melting properly over various colors and makes of underglaze. It does not sound like you have time to test, but it is really the only way in my view to get an expected result. We spent a whole summer testing and finally made our own clear gloss and matte that melted well over various colors, thicknesses and brands so our brush artists could paint, blend, shade in a normal fashion without too much worry.

I think if you post the recipe there will be folks here advocating calcining high shrinkage components if present, rather than adjusting the viscosity. You will definitely get ideas. Maybe repost as how to fix a glaze that crawls?

If your glazes like it, 6-6 1/2 hour firings are fine and not overly fast. If your results tend to be better with longer firings, then by all means easy to slow down. If you make very heavy sculpture etc…. Then slowing down may be a concern. My normal wares can go very fast with good results. Effective bisque firing is dependent on time, so some clays perform better with a long schedule to burn out all the organics. Easy to slow down though, just extend your switching times.