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About Min

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    full time potter

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  1. Blistering / What Causes it?

    I agree with what Magnolia Mud Research has said about looking at your firing schedules, both for bisque and glaze firings. Do you use witness cones to verify the firings? I found this image of the same glaze, looks vastly different from yours. I know you said your picture is deceptive but there is a huge difference between your glaze surface and the one from the link. Given the silica:alumina ratio I would expect it to be a high gloss when fired to maturity. Leaves me to think that you have two issues going on here, firstly the bisque firing wasn't thorough enough to burn out all the gas producing materials and secondly the glaze firing didn't get hot enough. Clean and slow bisque firing with as much ventilation as you can get, (vent the kiln or peeps out for most of the firing if you don't have a vent) to cone 04 plus verify your glaze firing with cones, add a soak just below your top temperature to allow time for the pinholes and blisters to heal and smooth over.
  2. are these engobes ?

    Both a slip and an engobe can change the surface texture and colour of the clay to which it’s applied to. An engobe is similar to a slip but is made with less clay content than a slip. Typically slips are formulated to be similar to a claybody in chemistry (or the clay body itself is used to make a slip). Since there is less clay in an engobe it is going to shrink less than a slip therefore can be used on leather-hard, dry greenware or bisque without shrinkage problems. Slips work best when applied as soon as possible to the still wet or damp clay pot so the slip and the pot shrink together. Engobes have higher flux content than slips to help create a bond between the clay surface and the engobe whereas a slip bonds to the surface through the interface between the damp clay and the slip. Slips don't rely on additional fluxes to bond with the pot. Since there is more flux in an engobe than a slip the fired surface can be more vitreous than a slip . I think part of the confusion comes from the term "vitreous slip" which by definition it is an engobe and not a slip. Underglazes can have a clay base or a frit base but with either they still have the properties of an engobe more than a slip. Others may have different definitions, this is my understanding of the terms.
  3. Away for a few days, cabin up the coast, wifi can be spotty where I'm going. 

    1. terrim8


      Have a nice time!


  4. Newbie without bentonite

    Whiting is calcium carbonate which acts as a flux. To opacify, zircopax, tin or sometimes titanium dioxide is used. edit: Pres linked a glossary to the top of the Studio Operations and Making Work section, it's a good place to look up materials etc.
  5. Thanks for posting my question Pres. hanging planters for succulents
  6. Sounds like it's just the wax burning off. Is your kiln vent working okay? Welcome to the forum
  7. Best Way To Reglaze

    Some glazes can really run when you refire them or layer two glazes, if in doubt put the pot on a scrap waster piece of bisque so if it does run it won't run onto your kiln shelf.
  8. Looks like there is some plaster film stuck to the clay. I would toss the trimmings that have plaster on them. Glad it worked!
  9. This topic has come up a couple times, link to one of the threads here. I can't recall ever seeing a list of ceramic chemicals that are teratogenic but that would be an area I would check with a medical professional about.
  10. Jerry Bennett workshop handout for making paper clay here, it covers pretty much everything for making paper clay. For the pulp I know a lot of potters use cotton linter rather than paper cellulose. I would be inclined to try it without molochite first. Welcome to the forum
  11. @AscotLady, if you don't like the way it looks now you really don't have anything to loose by refiring to the correct temperature. If it's a large or thick sculpture I would heat the kiln very slowly, especially through the 530 to 600C range.
  12. Since the pots you fired to cone 10 are no longer porous it's going to take a lot of time and patience to glaze them and the task will be more troublesome than its probably worth. Warming the pots up to around 180F will help get the glaze to stick. If the pots are very precious to you it might be worth the effort but otherwise I would chalk this up to a learning experience and start over. Yes you can use your cone 6 glazes on your pots that have been fired to cone 10, they will need to be fired to cone 6. Going forward I would use a cone 6 clay with your cone 6 glazes. Firing to cone 10 in an electric kiln will wear your elements out much faster than going to 6. Welcome to the forum!
  13. If you have a shallow basin wide enough you can dip it horizontally so you won't need as much glaze, a couple inches more than the depth of the plate should do it and wide enough to be able to skim the plate into and out of the basin. Staple removers with the prongs filed down so they will fit on the rim of the plate (or tiles or lids etc) one on each side and skim it through the glaze. The filed down prongs just leave tiny little snake bite type marks that are easy to smooth over. (btw your glaze looks like it needs to be sieved to get those lumps out or mixed up some more before dipping)
  14. Test firing my new kiln

    Are the instructions on pages 3 and 4 of this what you have? With a brand new kiln I would do a very slow first firing to bisque temperatures plus a very long soak at the end, I would also leave the peephole plugs out for the entire firing if you are not using a kiln vent. You can verify temperatures with cones when doing this firing, just do it when the kiln is approaching your target temp / cone. I would also put your cone pack on a waster scrap of clay if you do a very prolonged soak.

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