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I like throwing that clay but it made my skin itchy. Have you found this? I like how nice and tight it is, have some mugs and bowls made from it, parts unglazed and no staining after many years of everyday use, slip made from same body without sand brushed on unglazed areas.

Hi Zuri and welcome to the forum. I looked up the Lavafleck and see that it has a firing range of 1200 C - 1270C. Clay is at its strongest when fired to maturity so if possible I would suggest raising the 1240C that you currently fire at. (and adjusting glazes as necessary)

I use 4 main glaze colours for dipping glazes, all made from one base plus a clear liner, these are in 5 or 6 gallon buckets plus an accent glaze that is just a small container of glaze. When I used to spray glazes I had more glazes but could mix up smaller amounts of them since I didn't have to have a big bucket to dip them in. I find that using less colours makes a more cohesive looking display, I don't try and please everyone by offering every colour under the sun.

That's how I feel too and probably why I have stuck with ceramics for so long. So much too learn and experiment with, one lifetime is barely enough time to scratch the surface. I am especially interested in the chem side of ceramics because I always want to know the why of things or what happens if ... Ever since I can remember I have had my hands in something. Started with textiles (batik, weaving, sewing) then wood (furniture) then clay. Thanks for posting my question Pres.

My suggestion for a QOTW would be what other creative things are you involved with? Thanks to @Hyn Patty for sparking this question with her post here where she said "But I also do a million other things too. Sculpting, mold making, resin editions, oil painting, etc and not just ceramics."

Thanks Tom and Bill, I do have diamond Dremel bits and diamond pads plus the green silicon carbide grinding wheel so I'm sure one way or the other I can get it sharpened.

Trimming tool I mentioned above arrived yesterday. Edges were hardly sharpened at all. I gave it a try this morning, not great. I'll try sharpening it but definitely will not be buying another.

Appreciate the people who have shared their recipes for a clear glaze. Getting a well fitting clear is one of the harder glazes to come up with. For those new to mixing their own glazes, be sure to test the glaze for FIT before making up a big bucket. Glaze fit to a claybody is no different than fitting a pair of jeans. What fits my body won't necessarily fit everyone else's body. If you use a high expansion glaze on one side of a pot and a low expansion one on the other there is a good chance of the pot dunting / cracking. If someone is looking for a clear glaze to use with or over stains or underglazes or some specific colouring combinations (like chrome tin pinks, reds, purples etc) then you need a specific type of clear glaze that is hospitable to the colourants.

A for effort Pres! Appreciate that it must be hard coming up with a new question every week.

Hi @Triciachapman and welcome to the forum. Just to confirm, it's the same make of slabroller and just the bottom roller isn't turning. If you slowly hand spin the bottom roller you will see 2 small set screws near both ends of the roller. Are they still there or is one or both missing?

@ChristopherW, I would not expect the recipe you posted to make a durable glaze. (but it will be a very expensive glaze to mix up given the price of Gerstley Borate now)

Agreed it's best to test small amounts before trying to alter an entire 5 gallons of glaze. Adding silica works up to a point in glossing up a glaze but if the amount of silica needed exceeds the amount of fluxes that are present to dissolve the extra silica then you reach a point where excess silica can't be taken into the melt. Worth a try but might need a plan B if it doesn't, this would be adding more flux along with the extra silica.

Hi JLR and welcome to the forum. Going forward you might want to consider applying the underglaze on greenware instead of bisque. I understand you wanting to save this load but not only is it tricky underglazing vitrified clay you are also going to have problems glazing the pots as glaze doesn't like sticking to vitrified clay either. Sometimes we just have to move forward and start again.

For a large piece I would roll out a slab of the same clay as your sculpture is made from, make it about 1/4 - 3/8" thick then cut strips of it about 3/4" wide. Dry the strips between boards (or drywall pieces or whatever). When you go to fire your sculpture lay the strips down first, gaps between them, and sit your sculpture on them. (don't need to bisque fire them but make sure they are bone dry before firing and fire slowly) What you are trying to do is raise the piece off the shelf and allow air circulation underneath the piece to help even out the temperature. Re slowing down between 1000F - 1100F both when heating and cooling, it's at approx 1060F that quartz inversion happens. As the quartz crystals change from an alpha crystal structure to a beta one there is a volume change of 1 - 2%, this can stress the clay and cause cracking / dunting.

Hi and welcome to the forum. I would look at what the slow glaze program is going at during the 1000F - 1100F range, if it's more than 50F / hour then I would slow it down during that ramp. I would also slow the kiln down during cooling during the same range and not open the kiln until it's at room temp. This is something I would be looking at doing to help equalize the temp within the kiln and doing it slowing as that is a large piece and there will be substantial differences between the 1.5" thick areas, where it sits on the shelf and thinner areas. If you aren't sure what your glazes will do in a slow cool then I would suggest running some test pieces through the firing before your large sculptural piece. I don't know what your final cone is that you are firing to but another option would be to fire it to your target cone using the slow bisque program instead of the slow glaze program then add a slow cool. Look up your make of kiln and what the preprogrammed firing programs are and compare the two. (I'm going to delete your duplicate post in the Chemistry section)

Or you could use Pieter Mostert's Brongniart calculator. You need to know the weight of the glaze materials within the glaze slurry. Brongniart's formula works this out, either longhand or with the calculator. https://pietermostert.github.io/SG_calc/html/brongniart.html

Just to confirm I'm reading this right, the clay is cracking as it's shrinking on the wood mold/frame? You are keeping the clay wet?

Is the glaze made for brushing or dipping?

I bought one of these from Bailey quite a few years back, can't remember if it had a blue haze on it when I bought it but it definitely rusts. They are calling it a Scraper Rib, it's steel, but not stainless and not flexible. https://www.baileypottery.com/c-128-048.html

When I enter the MC6G High Calcium Matte 2 into the EU calculator I'm not seeing excess to the eutectics of CaO even though this is coming in at 0.90 in the UMF. I'm going to assume this glaze uses a different matting mechanism, perhaps the excess alumina and silica causing the matting or a micro rippled surface. If that's the case we need another recipe to test the theory with or reduce the silica and alumina perhaps.

I'll plunk it in and see what it shows. If the EU calc shows excess silica (like I assume it would) then yes. edit: I'll use this recipe to play around with. (without any colourants)

Yup. @Suresh Sundaram, your video clip is showing mocha diffusion. If you go to the link @Hulk posted Hopper explains the process he is using. Quote below from it. Note that Hopper used a lowfire chrome red lead glaze for the red, chrome is well know to be volitive in the kiln. To recreate that look a cadmium inclusion stain could be used in a glaze or slip to get a similar colour instead of lead and chrome but probably wouldn't get the halos. "IN THE SOUTHWEST SERIES, THE DRY GREENWARE FORMS ARE SPRAYED WITH WHITE TERRA SIGILLATA, POLISHED WITH A SOFT CLOTH AND BRUSH DECORATED WITH A VARIETY OF BRUSHES USING BLACK-BRONZE PIGMENT. THIS IS THEN FIRED TO CONE 9 IN OXIDATION. THIS IS FOLLOWED BY PAINTING AND TRAILING WITH A CHROME RED LEAD GLAZE AND RE-FIRED TO CONE 010. ALL FIRING WITH THIS SERIES IS DONE IN AN ELECTRIC KILN IN OXIDATION. SOUTHWEST SERIES PIECES ARE PURELY DECORATIVE AND NOT FOR FUNCTIONAL USE."

@PeterH, using your train of thought... If a high calcium matte glaze recipe was put into the EU calculator then the calcium in the recipe reduced until the EU calculator showed no excess calcium then in theory it would be a gloss when slow cooled. I'll try plunking MC6G High Calcium Semi-matte one into the EU calc. and see what happens to the flux ratio. I'll try it with both wollastonite and another recipe with CaCO3 and see where the flux ratio lands. (might be tomorrow before I get to it)

@Christy Ann, like others have said underfiring a bisque isn't usually too big a deal but going forward if you use a "dirty" clay, like one of the dark brown bodies with lots of manganese or a red clay body, you might want to try bisque firing to cone 04. The extra bit of heat helps burn out more of the impurities as does doing a slower firing. (this helps avoid some glaze issues) It's hard to tell how a cone 6 glaze firing is going to go based on a bisque firing. Being thoughtful about how you load the pots does help. As a general rule of thumb electric kilns will fire cooler at the top and bottom and hotter in the middle. To avoid underfiring top and bottom areas load less mass in these areas, this means taller pots therefore less shelves. If you have shallow / short pots load them in the middle of the kiln using more shelves. Some people like to watch cones towards the end of the firing. To do this you must use proper eye protection every time you look in the kiln. (like these ones) If your target is cone 6 then you would place 3 cones in front of the spyhole(s), cone 5 (sentinel cone) cone 6 (target cone) cone 7 (guard cone). Once you see cone 5 tip down then expect cone 6 to be down in very approximatley 20 minutes. (depends on element life and kiln size). Having the guard cone will let you know if you overfired and by how much. It can be very awkward to see cones so not everybody likes doing this, above all be careful if you do. Just need a quick look, don't sit in front of the kiln and watch them fall. If your Amaco glazes have a recommended firing going to cone 6 then I would put the kiln on low for 2-3 hours, then medium for 2-3 hours then high until you reach cone 6. One thing that can make a difference in when the kiln sitter trips is how you place the cone in the sitter. If you find the kiln is underfiring (if only using the kiln sitter to shut off the kiln and not looking at the cone pack) then move the sitter cone over just a bit so the bar rests on the thinner side of the cone and the opposite for overfiring. Some people much prefer using sitter bars rather than cones so they are more consistent in how they bend and positioning doesn't matter. Like Jeff mentioned it's also possible your sitter needs adjustment. Easy to do if that's the case, video here showing how to do so if you need it.

What is your firing schedule for bisque? Also, are there more pinholes on trimmed areas? Once the pot is thrown do you rib the outside? Any chance you have some other clay handy that you can try the glaze on?