If you think its from firing and not a cooling crack then slow down the temp rise during the inversion zones. (I would also slow it down when cooling through these temps as platters like to dunt when refired) So slow down the firing starting at about 1000F up to about 1100F and to be safe you could slow it down from 400F to 500F also.
My guess would be from moisture getting into the clay through repeated dishwasher, hand washing and just plain usage. The accumulated moisture is getting hot as it's heated in the microwave. You could do an absorption test on the clay to see how porous it is. What clay are you using and do you know for sure it was fired to ^6?
am i the only person who thinks that video is one of the worst i have ever watched? the technique was a poor way of doing anything, the slip was not colored so why use it at all and the scraping of clay in a room full of people breathing the stuff in was the dumbest safety violation i remember anywhere. is it just me?
The lady in the background with the double jointed elbows was kinda interesting.
Thought I would share what I have found to work for marking test tiles easily and cheaply. The Dixon (Hi-Heat) China Marker pencil in brown lasts through ^7 oxidation firings on my test tiles. It stays clear and legible and is way cheaper than the ceramic underglaze pencils. ($7- for a dozen china pencils on Amazon versus around $12 for one ug pencil) It's kind of waxy so doesn't smear or rub off if you wipe glaze drips off bottom of test tiles. It doesn't leave any ghost marks on the kiln shelves.
It does burn out with glaze overtop but for test tiles it's brilliant. Haven't fired it hotter than ^7 so don't know if it will do ^10 but I think it would.
I plunked the recipe into Insight and played around with increasing and decreasing the ingredients just in case you made an error in the weighing out like you mentioned was the possibility. If you had put only 10 silica in and 30 spodumene then the Si:Al ratio goes from 8.57 to 6.38 which along with the slow cool could be enough to make a matte glaze. Also, if the error was with the OM4 ball clay the the Si:Al ratio is 6.37 ( 10 silica, 30 ball)
Does it feel like an alumina matte, or a silky / buttery matte?
I would include a test tile with no colour additives as a baseline.
Also, do you need to slow cool if you are going for a gloss?
I think there are potter's pots and potters' glazes and pots fort he general public.
I use my potters' pots and buy potters'pots but my best sellers are not to my taste.
I do "like" them at the level of, well they work and are well made, just do not feed my soul.
Schitzo here .
This is the thought I have every time I use a blue glaze or slip. Blue sells, I need to sell pots therefore I make pots with blue. I don't have a single blue pot for our use in the house.
I would much prefer to make carbon trap shino glazed ware, wood or soda fired but it also comes down to what firing methods are available to me. Living in the burbs I don't have the option of firing a gas kiln let alone a woodfired one.
They are soluble salts that have precipitated out of the glaze. After sieving the glaze take all the gritty rough bits and put them in a cup and pour in enough boiling water to dissolve them. Add this back to the sieve and it should go through. Might need to let the glaze evaporate a bit to get it back to the right consistency.
@Tyler: I have come across crawling issues, yes. I just sorta have learned over the years what it does and doesn't prefer--like super thick application, as you said. I also noted that it needs to be mixed really, really thoroughly. Aaand, the stuff on the bottom of the bucket likes to crawl the most. Maybe because the GB is of a higher concentration down there... I wonder if the ratios could be tweaked a little.
Do you want to try a simple experiment to reduce crawling but keep the chemistry exactly the same? Calcine a small bowl of epk next time you do a bisque firing and try subbing part of the regular epk for calcined. If you take out 1/2 the epk the new recipe would be:
Calcined EPK 12 point 5
Less shrinking of the glaze (from the EPK) equals less crawling.
Your work is gorgeous! I think that when we are putting our work "out there" most of the general public don't realize what offside remarks can do to the ego, if you let them. You gotta know your work is good, if your illustrations are your strong ability then play it. Just off the top of my head I'm thinking red clay murals with your illustrations would be amazing! If you live in an area that doesn't have a lot of support / cash for art then get some good images and send them off elsewhere.
Remember the old kids storybook, The Little Engine That Could... I think I can, I think I can but change it to I know I can, I know I can.
In addition to the great ideas in the link from Chris you could add the metal post firing. For screws & hooks I guess you would need to modify them but if you have access to a welder seems doable. The pics are of Hanaire ring and hook from Japan Pottery Tools in San Fran.
I'm not to keen on the idea of using a ^10 glaze at ^6, for it be mature at the higher temp it's going to be underfired at the lower.
If you haven't already got it a good book to learn the basics of glaze chem is Mastering Cone 6 Glazes by Hesselberth and Roy. There is a chapter in there about figuring out what COE or CTE (coefficient of thermal expansion) will fit your clay without crazing or shivering. Glaze calculation software is a big help too but more of a learning curve than reading the above book.
Test tiles are your best friends! Make lots and lots of them, and take the time to test your glazes on each of the clays you use.
If you are looking for a white glaze for functional food bearing surfaces then a glossy clear plus about 10 - 14% zircopax will give you a clean crisp white. Zirconium (the stuff zircopax is made from) also has an extremely high melting point so that when you add it to a glaze it actually helps reduce crazing. If you want a softer white then tin oxide, or a blend of zircopax plus tin oxide.
I would chalk that glaze load up to experience and move forward.
I'm not big on handing out random recipes since your materials, clay and firing schedule are going to be different from mine but here are a couple basic white glazes that fit mid expansion stoneware at ^6 quite well if you want to include them with your tests.
Came across a blog that describes how in France huge terra cotta pots are made using a heavy rope wrapped sectional armature. The armature is made to be removed prior to firing. This method hasn't changed in hundreds of years.