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tinbucket

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  1. Another way to achieve the same thing as adding powdered clay (if you don't have any) is to evaporate some of the water from the deflocculated slip. A wide, low container will give more surface area to evaporate the water and achieve the desired consistency.
  2. I believe what you are seeing is the grog/sand in the clay. If you look in the lower left of the tile you can see bubbles where the glaze has dripped/pooled. Yes, I agree, thinner mixing and application is better.
  3. https://glazy.org/recipes/20547 Try this glaze. Derek Au has tested it on a brown stoneware and there is a picture in the link. He has tested many cone 6 clears and most of them cloud on a dark body. The determining factor from my point of view seems to be the boron level. This glaze has 2x the amount of boron necessary for cone 6, which will diminish the glaze's durability long term. If you want to see the other glazes he has posted click on his name, his tests are a great resource for us all.
  4. Derek Au and Jake Corboy have tested an extensive number of stains in glaze and clay. The base chemistry can affect the color of certain stains (glazes with magnesium can turn chrome/tin [maroon to pink] stains grey) but this should give you a general idea. Scroll to the bottom of the page to see the different stains. These are all cone 6 oxidation. https://glazy.org/recipes/34778 https://glazy.org/recipes/18705 https://glazy.org/recipes/30094 Jake Corboy's website https://www.jakecorboy.com/all-testing-info This is an excellent matte glaze and there are a number of different stains tested if you scroll to the pictures at the bottom. https://digitalfire.com/4sight/recipes/matte_glaze_base_for_cone_6_121.html
  5. I have also read that in Andrew Martin's book and I have had great experience using Grolleg in casting slip. Another thing to consider is that Grolleg has some potassium (flux) and EPK does not. EPK will require more added flux to reach the same level of vitrification for an equal amount of Grolleg. Not sure if I read this on digitalfire or Martin's book but this way to mix casting slip works well for me: mix your slip, let it sit overnight, measure specific gravity, add water to reach target specific gravity, then add deflocculant to adjust the fluidity of the slip.
  6. You might try contacting potter Samuel Johnson. He had one listed on instagram a while back. His instagram is @samueljohnsonpottery and his website is samuel-johnson.com. Another person to ask is Adam Field.
  7. How are you mixing your clay? Something that has not been mention is that commercial clays are typically pugged in a de-airing pugmill. This alone makes the plastic clay much more dense than if it was mixed to a plastic consistency from dry materials (Soldner mixer). Mixing clay in a slurry and drying out will produced a more thoroughly wetted and denser clay body but it is much more work. If you are mixing in a Soldner style mixer there will be a lot of tiny air pockets in your clay. I have not read this anywhere but I have noticed it from my own experience...maybe others can confirm or deny. Either way, a vacuum de-airing pugmill will produce the densest and most homogenous clay body.
  8. In the meantime, you can read these sources online which I have found to be very helpful. The first two links are articles written by Matt Katz and others. UMF may seem very difficult to understand at first but once you understand the general concepts it will be very helpful in your glaze formulation. I recommend looking at Glazy.org, especially the calculator function. Glazy is great because it tells you what oxides (silica, alumina, sodium, calcium, etc.) and how much of each is being contributed by the glaze materials. The calculator allows you to adjust material amounts and see how the chemistry changes in real time. It can all be very overwhelming but the more you read the more you will understand and have control over your glazes. https://www.ceramicmaterialsworkshop.com/reports--publications.html https://ceramicartsnetwork.org/wp-content/uploads/2008/10/TF_BoroninGlazes_0912.pdf http://help.glazy.org/concepts/analysis/#unity-molecular-formula-umf https://digitalfire.com/4sight/troubleshooting/index.html If you are more of a visual learner, it may be helpful to do a Currie grid test of a glaze you like. More information on that can be found below: https://wiki.glazy.org/t/currie-grids/183
  9. 2-3% lithium carbonate, pearl ash, soda ash, or borax can flux the glaze more (increase melting) and may improve the color response. If you don't seive the glaze after you add the material (just blend well) then you will be left with some crystals which will create some localized fluxing. I would not recommend any of this if you were making functional pots. I understand calculating percentage may be a little complicated since you are starting with a wet glaze. You can either add x dry to a cup of glaze, test, then adjust or calculate the amount of dry material in x amount of wet glaze by measuring the specific gravity. If you look at recipes for texture/sculpture/special effects glazes you will notice trends in the materials used and amounts. This will give you a starting point if you are looking for a particular effect.
  10. Can you give us some more information? Cone? Color? Recipe? Here are some ways to make a glaze matte: Increase alumina, decrease silica, add calcium, add magnesium
  11. @kathleencorcoran I have used Redart sig on bisque, then fired to cone 6 with no problems. This may be different with more refractory clays (ball clay/white sig). Sig is very opaque (I think because of the fine particle size) so you do not need a lot to cover the clay body. You can experiment with different thicknesses but I would try to use it the same way you would on greenware. Since you are pit firing the sig may adhere better to bone dry clay
  12. As Neil and Magnolia said, I believe it is either volatile or soluble fluxes. Some glazes do this more than others but especially those with higher amounts of Neph Sy, Lithium Carbonate, basically any on the alkaline fluxes/feldspars high in sodium, potassium, and lithium.
  13. Glazes will look a little brighter and the body will be more white and glassy using porcelain. These are generalizations and it depends, of course, on the formulation of the body. If you are comparing white stoneware vs porcelain in reduction, transparent glazes will look far better on porcelain. Porcelain is generally less plastic and more thixotropic/more difficult to work with. It's a trade off, workability for whiteness/translucency of the body and brightness of the glazes. I say make some of your work with 25-50 pounds of porcelain, 2 different clay bodies if possible, glaze it, and then assess the results. The only way you will know is to try it. There are many nice white stonewares out there but in my opinion porcelain has something that stoneware does not. Many times the compromise of workability is not sensible but it really depends on the type of work you are making and the glazes you use.
  14. Another thing to consider is the clay memory. Porcelain remembers. Say you remove a leatherhard pot from the mold and put too much weight on one side of it (imagine holding a cup sideways). Even if the pot does not go oval in that moment it may be enough for it to cause warping later on. However I suspect this is a problem with uneven drying, even a little bit can cause significant distortion
  15. Are your pieces warping in drying or firing? Evenly drying will take care of most drying warpage, I think. If your porcelain has a high amount of plasticizer this can require more attention. If your work is warping during the firing >>> Do you mix your own casting slip? How important is translucency to your work? Although changing the form will help I think the pyroplasticity of the porcelain is a more important factor. I think many porcelains are over fluxed to make them more translucent (a broad statement). For example you may be able to reduce the amount of feldspar in your casting slip, maintain 0% porosity, and reduce the pyroplastic deformation of your pots. Another option is adding a filler such as pyrophyllite or alumina. From what I have read potassium feldspars create a more viscous melt than sodium feldspars (custer will deform less than minspar in an equal level of vitrification). If you test/mix your own casting slip you will have much more control over the warpage of your pieces and have to compromise the design of the form less. I'm in over my head, calling on @glazenerd
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