Hulk

Thank you fights for the quick answers! @Min I have made similar observations, the glaze that showed significant less gloss after the 6 hour boil has also been in the dishwasher almost every day for about 6 month now without any change in appearance. So I also feel like this test might just be too harsh. I wish I would have a put a regular porcelain mug from the store in too just to see how a commercially made one would hold up. 
 
@Callie Beller Diesel thanks for the warm welcome. Interesting that colorants do seem to have such a strong effect, even with good base recipes. Makes you really think that you always need to run tests even if it looks good on paper. Fingers crossed that you will be successful with the line blends. 
 
@Bill Kielb I agree that not all glazes are winners even when they look good on paper. I feel like though that maybe this test is too harsh because other glazes (variegated slate blue from mastering cone 6 glazes and a stable glossy glaze) also suffered through this test. Going more into the direction of glossy would be a good idea but I am trying to create a satin finish with the 6:1 ratio + slow cool. Thanks again for your time and Input 

Spent a huge part of summer getting ready and moving and now firing a new to me Geil 18 cubic foot downdraft kiln.
It started years ago when I found this kiln for my self and a potter fiend I know said he wanted it so I let him buy it and ship it up from LA. He fired it twice and passed away. I promised his widow to clean out his studio which I did a few years ago and this summer finally made moved the kiln (it weights about 2,700#s)
It require me knocking out some support collums and putting in two 20 foot LVL beams so I could open up my kiln area out under a huge metal roof area. Once the beams where in We moved the small 12 cubic updraft out of the way and I jackhammered out the column supports I poured in 1974. And made large cement pad -about two yards of concrete -I had a pump truck pump it into our space. I added some small wings to the main pour a few days later exposing in more rebar for the kilns to set back from one another more. I had to deconstruct a wall at kiln site in his kiln room and spent 3 days getting kiln out onto a specialized equipment trainer with a pallet jack .The trailer  jacks down flush with ground level to put kiln on and made a solid wood support structure in girl kiln (floor sides and arch support to move it the 15 miles. Here at home it landed on the street for 5 days and  derusted then painted it where it needed it and had a local yard move it with a forklift to my pad where I again used a pallet jack to fine tune it and the other kiln. Of courseI had to move my gas lines before the concrete went in and got two 1 inch line stubbed up from my 2 inch lines underground that run through my kiln area. I had to change out 15 orfices in the Geil (drilled them out with super fine drill buts) as the kiln was propane and now its low pressure natural gas. I tried to fire all three kilns at one a few weeks ago and did not have enough gas to do that but I did fire the Geil and my car kiln two days ago with no issues. I was abal to put both my peter Puggers on this slab as well and now that can move around with ease. The whole area is way more efficient now and I did I had done this 10 years ago. The Geil sips gas but now i must order 14  new 14x28 advancers as the old shelves it came with are just to thick and heavy and warped for my old body. Those shelves will cost as much as I paid for the kiln and will take 3 months to ship here from Germany (thru bailey). I am unloading my second glaze fire today from the Geil and I have bisqued in it twice as well. The auto pilot system has a few bugs but I'm working thru it.

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

You run a higher risk of having blisters or pinholes unless you re-bisque to the temperature you know works. 

I'ld do it again to your usual cone once you have your kiln sorted out.

@Christy Ann, while you are doing your testing I would suggest doing some absorption tests with your claybodies also. Manufacturers post absorption figures but it's best to do your own testing since those posted figures can vary from actual results using our own kilns and firing practices. Info on how to do a calculated absorption test on this link about 2/3 the way down. Given the posted absorption figures are fairly high for the clays you are using and typically ^6 and ^10 work isn't glazed on the bottoms (like lowfire or earthenware usually is), this is relevant. As has already been said the absorption figures for functional ware at mid and high fire should be below 1 1/2 - 2%.
While you can get a well fitting non crazing glaze for pots fresh out the kiln they should still be stress tested for delayed crazing also. When functional pots (with higher absorption) is used it soaks up moisture from use and from doing the washing up. This moisture enters a porous claybody causing it to expand ever so slightly. (especially when heated as in a microwave) When the claybody expands two things happen: one is the clay can become very hot, as in too hot to pick up a mug by the handle, and secondly the glaze will more than likely craze. This is called delayed crazing. Delayed crazing can also happen over time even without using the pot if the absorption is quite high by atmospheric moisture.
edit: to stress test for delayed crazing put some samples (fired in different areas of the kiln) into a 300F oven. Leave them there for 20 minutes or so then plunge them into ice water. On a clear glaze if there is crazing it should show up, if unsure cover it with a felt pen then wipe it off. (or use calligraphy ink if you have it)

The software I'm using (Glazemaster) calculates COE 6.52 for that glaze, which, if all things were equal, would craze on some of the clays I've tried (and no longer use...), and maybe craze on one or more that I use now.
However, all things aren't equal!
My understanding is that:
  a) calculated COE is especially helpful when adjusting a recipe, where the ingredient ratios are adjusted, and/or a new ingredient is introduced;
  b) calculated COE is less helpful for comparing glazes that have radically different ingredients/recipes, where a glaze with a lower number may craze more than one with a higher number.
My own experience supports both notions.
I'd started over several times in my quest for a well-fitting clear.
The sodium and potassium were lowered, and lowered again; talc was raised, and raised again; lithium was introduced - via petalite, close, a bit more talc, a smidge more petalite, voila!'
I've posted the recipe here somewhere; if you're interested, OP, shout. No guarantee it would work with the clay in question! GlazeMaster calculates COE of 5.31

The software I'm using (Glazemaster) calculates COE 6.52 for that glaze, which, if all things were equal, would craze on some of the clays I've tried (and no longer use...), and maybe craze on one or more that I use now.
However, all things aren't equal!
My understanding is that:
  a) calculated COE is especially helpful when adjusting a recipe, where the ingredient ratios are adjusted, and/or a new ingredient is introduced;
  b) calculated COE is less helpful for comparing glazes that have radically different ingredients/recipes, where a glaze with a lower number may craze more than one with a higher number.
My own experience supports both notions.
I'd started over several times in my quest for a well-fitting clear.
The sodium and potassium were lowered, and lowered again; talc was raised, and raised again; lithium was introduced - via petalite, close, a bit more talc, a smidge more petalite, voila!'
I've posted the recipe here somewhere; if you're interested, OP, shout. No guarantee it would work with the clay in question! GlazeMaster calculates COE of 5.31

We will do some tests. Thank you so very much! This helps 

This is interesting, in that the calculated COE is low enough that I wouldn't expect it to  craze  on any of the clays I use.  Regardless, my usual fix for glazes with too high an expansion coefficient is to add a bit of talc.  I'd begin with maybe 250 g talc added to the amounts you listed as a starting point and go up from there.

I remember seeing several "iron wire and golden thread" pots in the Percival David museum years ago, and they formed a lasting impression.
A couple of weeks ago I noticed that a crackle pot that I probably made in the 1980s had developed a significant number secondary cracks. But these cracks only visible when looking hard from a foot or so.  So I've been wondering if I should stain these secondary cracks with a brown "Indian ink". Although I'm not certain that the primary cracks are bold enough to give a good end result. 
PS From p585 of Ceramic Technology by Rose Kerr and Nigel Wood (Volume 5 part 12 of https://en.wikipedia.org/wiki/Science_and_Civilisation_in_China)
Perhaps the best evidence for the contemporary appreciation of crazing in Kuan and Ko ware is the occasional practice of staining the major glaze-crackle with an intense black pigment to provide a network of fine black lines on a smooth light ground. By necessity, this would have happened soon after the firing, and most probably when the wares were still hot from the kiln, when the craze lines were relatively open. Ceramics can continue to craze for days, or even for years, after firing,and this secondary crazing system often appears as a finer network on Kuan wares, between the major crackle lines. This secondary crazing is often stained a lighter colour, perhaps deliberately or perhaps simply through use. These two crazing systems supplied the celebrated "gold thread and iron wire" effect, so often admired in Kuan and Ko wares.  How the fashion for staining the crackle began is not known,but one possibility is that it was first used as a `rescue' process, designed to improve the appearance of accidentally oxidised pieces.

I love how curious you are about so many different techniques and styles! Stain the initial primary crazing then leave the pot for the secondary craze lines to develop unstained.

Anyone tried this double crackle effect with a Guan ware type glaze (also described as Ge ware, 13th/14th century AD - China)?

A kiln that's appropriate for the target temperature(s), that's one consideration, e.g., if you're working in midrange (Cone 5/6), a kiln rated to Cone 10 will last a good long while.
If you are working at the upper limit/rating of your kiln, having to replace the elements will come much faster.
For your testing, following a firing profile (time and temperature) that's similar to your big/production/main kiln is another consideration. A test/small kiln with a controller makes that much easier, otherwise you're having to hover and flip the switches on and off to replicate the firing profile...
Hope that helps!
...mainly, just wanted to "bump" your thread so you might get some responses...

A kiln that's appropriate for the target temperature(s), that's one consideration, e.g., if you're working in midrange (Cone 5/6), a kiln rated to Cone 10 will last a good long while.
If you are working at the upper limit/rating of your kiln, having to replace the elements will come much faster.
For your testing, following a firing profile (time and temperature) that's similar to your big/production/main kiln is another consideration. A test/small kiln with a controller makes that much easier, otherwise you're having to hover and flip the switches on and off to replicate the firing profile...
Hope that helps!
...mainly, just wanted to "bump" your thread so you might get some responses...

Montgomery College Rockville and Germantown Art Department 
Spring 2024 ArtWalk Collaborative Artist in Residence (AiR) 
Focus: Arts initiative for public, social, or community based outdoor visual arts projects using clay 
Project Stipend: $3000, travel and lodging not provided (non-residential) 
Project Length: Three weeks, March-April 2024 
Application Deadline: October 15, 2023
 
The Montgomery College Collaborative Artist-in-Residence (AiR) is a 3-week program in which a professional artist is embedded in the Rockville and Germantown Art Departments, providing the unique opportunity for students to work directly with contemporary artists other than faculty. Students have the authentic experience of creating artwork for public installation, as part of collaboration with peers, faculty, and the artist working toward a common goal of an art installation or social practice project. 
 
ArtWalk is two weeks of public art in which art classes install outdoor public art or lead participatory art activities on the Germantown and Rockville Campuses. The Spring Artist in Residence (AiR) will work with students both inside and outside the studio to create work that will engage students and AiR during the existing outdoor ArtWalk weeks on the Rockville and Germantown campuses. This collaborative work will use art and creative thinking to impact the community of students and should focus on projects that culminate in activities and projects to be viewed or participated in outdoors.  
 
We are seeking individuals or groups with a wide range of ceramic artistic practices, including (but not limited to) raw clay installations and video. Proposals should offer a mutually supportive creative learning environment between students, classes, and Artist. Professional artists or Artists Groups working with clay, who are interested in working with students are encouraged to apply. Preference will be given to applicants whose work and proposal expand on the working range of foundation level teaching. 
 
Candidates should submit a proposal for collaborative processes and programming that provides foundation level students with direct hands-on experience in the arts that is guided by the Artist. For complete details, visit: 
https://tinyurl.com/CollaborativeAIR Please address any questions to Amanda.Miller@montgomerycollege.edu     

The least intuitive part of collaring is the part where you have to speed up for it to work better. Other than that, some things to keep in mind are to make sure you do a small pull or a pass with a stiff rib in between collaring passes. 

Checked all around for any loose wires and found none.
Replacing the relays solved the issue. I completed a fast fire last night in just over 5 hours.
I'm still curious about this tho. I've always assumed mechanical relays will usually fail on or off - not in between. But if they half-fail like mine did, then aging mechanical relays it would seem can impact fire times. As they wear, would carbon buildup on the relay pads substantially increase resistance to the circuit? 

I find myself in the same boat. I am repeatedly drawn to low fire clay and processes and I’m not really sure why.  This forum hada shown me I’m not alone.  

Hi
I have made a  Torsional Viscometer 
 
I wanted something where I could measure the viscosity using a laboratory instrument as with anything like this t.ype of equipment can be very expensive I decided to use my 3D printer to make a fully working  Torsional viscometer. The viscometer is very accurate and every part can be replaced and upgraded.   Parts not printed consist of :-   Purchased from eBay   1. Stainless steel shaft. 1. Perspex tube. 1. Flywheel Top stainless Stainless steel disc.  1. Sample cup  small stainless steel disc. 1. Small disc in the base.    Thumb screws  bolts. (Brass - stainless steel)   1. 30swg torsion viscometer wire (This has been made in house   - wire ends are designed to be reused)             Printed parts:-   2. Support brackets .....................      (Hold the Perspex wire guard tube) 1. Scale gauge bracket ................     (Hold the printed vinyl scale) 1. Sample holder bracket .............     (Allows the sample to be held in position) 1. Sample stop ..............................     (This stop allows you to set the sample bracket height) 1. Main base ..................................     (The main base has 3 micro adjustable levelling)   1.wire holder ..................................    (Special wire holder bracket with micro adjustment) 1.Adapter ring ................................    (This was added so you could use a commercial spring wire) 1.Sliding centring wire guard ........    (This allows you to slide section of the wire guard to assist in levelling) 1.Flywheel ......................................    (Customisable can add stainless steel weight discs, brass locking screw for securing bobs) 1.Flywheel locking mechanism ......  (Fully adjustable indicator pointer locking holder)   2.Accessory trays ..........................   (designed to locate on the side of the main base to store any Allen keys and also bobs   1.Waterproof vinyl gauge............... (can also be used with removable logging dial)           I decided to build a 3D printed Torsion Viscometer to do some experiments with my hobby pottery glazes. I designed each part in Design Spark Mechanical CAD software . For the vertical frame. I used copper tubing as I had this lying around in a scrap bin. (This has  been replaced with a stainless steel round bar       
 

Hi s6x, welcome to the Forum!
Good questions.
I don't believe there's chemical considerations, given the clay is nearly the same as it was originally.
Thoroughly dry clay absorbs water quickly and turns to mush, even big chunks, total mush.
Damp clay bits get mushier on the outside, however, the insides seem to stay about the same for a very long time.
I'm storing clay to be reclaimed in two states, totally dry, and slop, nothing in between.
Eventually the slop will dry out to become a disc of dry clay at the bottom of the bucket - even with a lid.
Any road, to start, I'll put the two together, then add enough water such that the dry stuff turns to mush AND the result is wet enough that my grout mixer (driven by a 1/2" drill motor) can turn it without burning up.
I'll run the mixer for a few minutes - not so long that the drill motor gets hot (!!!) - several times/day until the mixture is smooth and uniform.
Ah, there's the point! Smooth and uniform mixture! Then I'm scooping out onto plaster slabs for drying to wedgeable consistency. When it gets there, wedge, bag, go.
Thoroughly dry, so the clay will absorb water quickly.
Mush, wet enough to mix with the drill motor setup.
And finally, whatever works for you!
With stronger machinery, the reclaim process can be done with less water? With a pugmill, the result can be dialed to target consistency, no drying time required?
I believe so.
Surely, a small amount of clay can be reclaimed without any mechanical assistance. I like to use the drill powered mixer.
 

Hi s6x, welcome to the Forum!
Good questions.
I don't believe there's chemical considerations, given the clay is nearly the same as it was originally.
Thoroughly dry clay absorbs water quickly and turns to mush, even big chunks, total mush.
Damp clay bits get mushier on the outside, however, the insides seem to stay about the same for a very long time.
I'm storing clay to be reclaimed in two states, totally dry, and slop, nothing in between.
Eventually the slop will dry out to become a disc of dry clay at the bottom of the bucket - even with a lid.
Any road, to start, I'll put the two together, then add enough water such that the dry stuff turns to mush AND the result is wet enough that my grout mixer (driven by a 1/2" drill motor) can turn it without burning up.
I'll run the mixer for a few minutes - not so long that the drill motor gets hot (!!!) - several times/day until the mixture is smooth and uniform.
Ah, there's the point! Smooth and uniform mixture! Then I'm scooping out onto plaster slabs for drying to wedgeable consistency. When it gets there, wedge, bag, go.
Thoroughly dry, so the clay will absorb water quickly.
Mush, wet enough to mix with the drill motor setup.
And finally, whatever works for you!
With stronger machinery, the reclaim process can be done with less water? With a pugmill, the result can be dialed to target consistency, no drying time required?
I believe so.
Surely, a small amount of clay can be reclaimed without any mechanical assistance. I like to use the drill powered mixer.
 

I use several types of rubbing stones -I have the 100 grit diamond pads like Min posted above from Tool city .com or Temu.com which has them for low cost
also like the pucks  from clay Planet
https://shop.clay-planet.com/the-puck-hand-grinding-stone.aspx
These are easy to hold as well although not as feather light as the diamaond pads which I take to shows
I also use the 3 block white stones from tile shops (youbreak them off ) as there are three in a long shape.
I do to much production to take pots to a spinning wheel so I never did that.
We rub the bottoms as we pull them out of kiln

Changing the mesh size of the silicon carbide apparently influences the appearance.

PS I suspect that refiring can only smooth/collapse/consolidate previously fired lava glazes, as all their fizz was expended in their first firing.
As the top half of the cylinders indicate thicker application of the glaze increases the foaming -- especially for finer grades of SiC.

In my experience it depends on what you're trying to reclaim. It's tricky to reclaim a whole bag of clay that has dried too much to use. There is a whole process of adding a little water to the bag, poking holes in the block of clay, then submerging the sealed bag in a bucket of water. Mine always comes out too wet on the edges and still firm in the center and is tricky to homogenize. 
However with trimming scraps and failed pieces, I just add them to a bucket in any form (dry, leather hard, intact, crumbled) and add CLEAN water (not slip) until they are all submerged. A couple days later I use a sponge to remove the excess water (why dry a bunch of extra water when processing) and toss the slop onto plaster. The plaster really helps to keep the clay at an even moisture level, more so than starting from a perfectly smooth slip.