I have been making my own glaze for a little over a year now. I am no expert, but have had good instruction. It takes hours and hours of testing and firing. Here is a video that I made following the way several potters that I know as well as some noted potters on you tube, Hsin-Chin Lin, and Simon Leach mix their glazes.
In your first video I'm not quite sure about why you are dry mixing the glaze ingredients prior to adding water. You are making a lot of dust unnessasarily, the silica dust will stay airborne for hours. It's not just the dust you can see thats a problem, there will be fine dust floating around for a day or so. Your jiffy mixer and sieving twice will disperse all the ingredients well without dry mixing. (I put the clay component in the bucket first then the heavy settlers after that then wet mix and sieve)
I came across this idea from the Digitalfire site, using the BatMate to hold down plaster batts. It’s sold to be used sandwiched between the wheelhead with pins and a batt to stop wobbling from loose pins or warped batts.
Since I never use batt pins with my homemade batts I have always attached the batts to the wheelhead with a pancake (or usually a ring) of clay. I found that the BatMate works really well at holding down plaster batts and the smaller sizes of wood batts, no pins, no pancakes necessary. I have used it with plaster batts up to 16” diameter with no movement of the batt. When trying it out with wood batts I’m finding that I can only use it with batts up to 8”. Any bigger than that and I push them off center. I don’t have any masonite batts so I’m not sure if it would work with those.
I dip the BatMate in water, squeeze it out so it’s fairly dry and put it on the wheelhead. If I don’t use too much water to throw with then I can throw for a couple hours before squeezing it out. If the BatMate gets too wet it’s harder to remove the batts. It seems like a fairly durable material that it’s made from, I had to pull up on a few times to remove the batts and there is no stretching or tearing of it.
The lid in the picture is on a 10” plaster batt, 14” wheelhead. (please excuse the mess, cleaning isn’t one of my strong points)
Just unloaded a bunch this morning. I agree with throwing them thicker than usual, the ones in my attachment are from 2lb 12 oz of clay. I do the cut-outs straight after trimming the bowl and dry them upside down. Cut-outs done with a scalpel (one of my favorite tools), holes with drill bits. ^6, smooth white clay, shrinks 14= 15%
I use the tapered ones. For sizing what I did was get one of those drafting circle templates that go up by 1mm diameter increments, roll out a slab of clay and cut out a series of holes (and mark the diameter) then fire slab to maturity. Plunk your stopper in the holes to determine the right size neck opening to throw, allowing a bit for glaze. When throwing the necks I taper it to the same angle as the stopper and measure the top.
When I first started spraying glazes I often put them on to thinly. I came across the site linked below; they take a different approach to determining how much glaze to put on a pot. They use volume of glaze per surface area of pot. I tried this for the first few kiln loads I sprayed glazes on to get a proper feel for what the glaze should look like to get the correct coverage.
If porcelain pots are sticking to shelves or in lid galleries the usual solution is to add alumina hydrate to wax resist. I'm not quite sure I followed what you are trying to do, firing unglazed pots touching together? If you really want to do this then brush the alumina/resist mix between pots at contact points. Approx 2 or 3 tsp per cup of wax resist.
It's a good idea to fire on a kiln shelf not directly on the kiln floor. A lot cheaper to replace a shelf than a kiln floor, plus the floor is usually a bit cool so raising it up 1/2" or so is a good idea. You can use a thin layer of alumina hydrate on your kiln shelf to prevent the the pots plucking, or use wax resist on the bottoms of the pots and put a shallow layer of alumina hydrate onto a flat surface and press the bottom of the pot into it before the resist has fully dried. The alumina will stick to the resist.
It just does not look like a kiln firing/ dampness problem ... It looks like a clay problem ... nothing exploded it just fought with itself. To me it looks like two different clays not totally wedged together but thrown in one piece and shrinking at different rates. Something's gotta give.
Exploding steam looks like something exploded and the evidence is usually all over your kiln. This is a stress crack.
I agree with Chris, it doesn't look like an explosion happened to the bowl unless you had some pots actually blow shards off.
My go to info on all types of cracks is The Potters Dictionary of Materials and Techniques by Frank Hammer. On page 82 he has a picture of cracks like in your bowl, brickwork pattern that is in the lower section of the bowl, hairline, and is a dunt caused by cooling the bisque too quickly. Stacked pots with a lot of mass on the shelf cooling much slower than the top section of the pot. Any chance you cooled quickly and or had stacked something heavy in the bowl? Were the pots on the top and bottom shelves more damaged than the ones in the middle of the kiln?
It wouldn't hurt to candle overnight and fire slowly until red heat until you have solved this but it really looks like a cooling dunt.
To get a really smooth nearly non beading surface I run a heat gun over the wax for a few seconds then wipe the wax with a piece of plastic wrap (saran or cling film), gives a waxed surface as good as hot wax does. The heat gun trick also works if you don't have time to let the resist dry, just be careful not to leave the heat on one area for more than a few seconds. Takes about 15 seconds to do the bottom of a platter.
Foam shops have scrap cut-off's, I have a bag of those which I cut off small strips of and dampen with water then use those to apply resist. I just toss them when done. (The firm density make good throwing sponges)
In areas like casserole galleries where the foam is awkward to use I use a damp, slightly soapy brush then rinse with hot water when done and put it through the dishwasher on the top level. (dollar store brushes)