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Min

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  1. The speed of the firing for the last 100C makes a difference in the final cone reached. If you are firing at 60C for the final hour 1260C is approx cone 9. If you are firing at 150C for the last 100C that is cone 7. Same temperature but big difference in cone reached. Now add on the 20 minute hold and you could very well be overfiring the glaze. Blisters are one of the trickiest things to sort out. If refiring makes the blisters worse then I'ld try a cooler firing. I'ld also strongly suggest that if you aren't already doing it to put some witness cones in your next firing.
  2. A few years ago myself and another potter were talking about Ron Roy's Licorice glaze with 2% cobalt carbonate. We both ran a base test (below) and put a piece of glazed ware in the dishwasher for 3 months. The base test did slightly remove some gloss whereas the actual running the piece through the dishwasher many times didn't. We came to the conclusion that the base test was too harsh a measure. Base test using soda ash to mimic dishwasher, use 50 grams of soda ash (sodium carbonate) to one litre of water, bring to a boil in a stainless steel pan and simmer for 6 hrs with the sample s
  3. Having enough silica and alumina in the glaze, not overloading it with colouring oxides (transition metals), and firing the glaze to maturity (not underfiring) are three major things to look at. So, firing with witness cones to maturity solves one thing, amount of cobalt is the second, and looking at the recipe on the formula level address the third thing. There are "limit charts" to give an idea of the range of silica and alumina needed to make a durable glaze. If the glaze is durable there is less chance of leaching. A couple limit charts below. You can see for high fire it's recommend
  4. Just to clarify, you are trying to maintain the curve? If so then yes, firing them in a form will maintain the curve but they obviously can't be glazed on the outside when doing the midfire glaze firing. Other option is to do the bisque firing to midfire glaze firing temperatures then use brushing lowfire glaze and refire to lowfire without the bowl form. Glazing mature clay is a pain and doesn't always work well but the gums in brushing glaze help it work easier than using a dipping glaze. Welcome to the forum.
  5. Interesting recipe Larry. I think that the term "majolica" threw me, was thinking tin base / opacified glaze, earthenware, on glaze liquid stain / oxide decoration type of majolica. May I ask why alumina hydrate to supply the alumina instead of calcined clay? Does it make a difference to the physical quality of the mix? If you left out the alumina hydrate, decreased the silica and perhaps bumped up the boron a bit it looks like it could make a cone 6 glaze. As it is it looks more like a claybody recipe with more diverse fluxes than is usually seen. (plus the opacifier) It's interesting
  6. Nope, not at all. I prefer full shelves because with the halves it takes more posts which take up shelf space. I also make quite a few large flat shapes which don't fit on half shelves so instead of mixing 1/2 and full and fiddling around getting posts to line up without the shelves wobbling I use all full.
  7. @catahoulacatie, if you do re-fire it I'ld suggest putting it on a waster thin slab of clay just in case the glaze runs again. PS - I like your online name, my Catahoula, Lou, from his younger days. (he passed a little while back at 18) Such wonderfully intelligent dogs.
  8. I'm a vertically challenged person too, my kilns are 37" and 38.5" tall with the lid open. I stand on an 8" tall stool to load and unload the bottom shelves with pots, it's not a big deal. What I think is more of an issue is bending over and putting the shelves in or taking them out. I use 21" diameter 3/4" thick high alumina full shelves, it is hard on the back lifting those in and out when you are short, stool or no stool. If I had to buy kilns/shelves again I'ld look at either a wider but shorter kiln or get Advancers or Corelite for the bottom 2 or 3 shelves. (I used Corelite shelves with
  9. @CharliesRadio, seems like nobody here uses that glaze. If you have time it would be best to fire a test tile with the glaze on it before using it for your dragon tea pot.
  10. Are you mixing it with the required amount of water for a dipping glaze or mixing it to a thick brushing glaze? Could just be that it's mixed way too thickly.
  11. If it's just glue added to what you have already tested in theory it should be okay to fire without issues, try a test and see. Have you read up on ceramic tape casting? I'm thinking it might have some crossover to what you are doing. In the pdf link from Alfred below they fire slowly up to 500F, don't know how necessary this is for what you are doing or how much glue you have added compared to the tests in the pdf, what you are mixing the glue with, clay, glaze or something else. https://static1.squarespace.com/static/527ac372e4b0d4e47bb0e554/t/527fd23fe4b0f7fd724aba83/13841086072
  12. Did you mean majolica glaze? PVA (polyvinyl acetate) glue + boron compounds cause the PVA to crosslink, sounds like you made lumpy slime. https://www.thoughtco.com/step-by-step-slime-instructions-604173
  13. If you don't know how refiring is going to effect the glazes it's a good idea to fire them on a thin waster slab of clay to catch any possible glaze runs. First glaze has already melted so refiring it can make it more fluid. Waster slab doesn't have to be bisque fired first, just make sure it's really dry. Another thing you might want to consider is placing the reglazed pieces in a cooler spot in your kiln. Some claybodies (especially porcelains and smooth stoneware) can bloat when fired a second time due to the body being fired with the extra heatwork. Refires are always a crapshoot but if th
  14. I think it's great you are thinking outside the box insofar as application method. If the same line quality is what you are looking for I'd make up some test tiles and try using your same method of acrylic paint plus cobalt oxide and give it a try on leatherhard greenware, bone dry greenware and bisque but run them all through a bisque before glazing them. (for the tests on bisque you probably only need to heat to about 500C to burn off the organics since they have already been bisqued but it won't hurt to re-bisque fire them) Give them a good wiping down with a damp sponge prior to glazing t
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