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tinbucket

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  1. tinbucket

    Glaze Chemisty Education

    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
  2. tinbucket

    Interesting additions to clear glaze

    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.
  3. tinbucket

    Make a shiny glaze Matt.

    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
  4. tinbucket

    Terra Sigillata Flaking Off

    @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
  5. tinbucket

    Toasted clay on unglazed side of rim

    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.
  6. tinbucket

    Porcelain vs White Stoneware

    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.
  7. tinbucket

    Porcelain Warping

    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
  8. tinbucket

    Porcelain Warping

    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
  9. tinbucket

    piping slip

    You might try adding a product called Additive A. It's an organic plasticizer and it is especially useful for extruding. I have not used it but from what I have read, it increases plasticity without increasing the water of plasticity. There is plenty of information online about it and many suppliers carry it.
  10. tinbucket

    Darvan swirl on slip

    Are you casting or applying slip to thrown pots? I have never heard of using deflocculated (Darvan) slip on leatherhard pots, only for slip casting
  11. tinbucket

    Irregular shape pot

    I would also suggest starting solid and carving away. If you want an angular form like that use a cut off wire or straight edged trimming tool to slice away. You can go at the block of clay with pretty much anything but I think it will be easier if you have some variation of the form in mind before you start cutting. Also! Look at Tim Rowan's work
  12. tinbucket

    silica

    I read recently (I think @glazenerd was citing someone else) that with improved grinding methods there is not that much difference between 200 mesh and 325 mesh. For glazes you want 200 mesh or 325 mesh. I think 200 is more versatile and the standard, if you have to choose one. The higher the mesh for any material, the smaller the grain size and the greater the surface area. For most (if not all?) materials this means they can melt more easily
  13. tinbucket

    Wobble pots

    Two more things that can cause wobbly pots: a lump of clay with varying moisture levels (needs more wedging) and releasing your hands from the spinning pot too quickly
  14. tinbucket

    Why is glaze blue

    Also maybe: https://digitalfire.com/4sight/glossary/glossary_boron_blue.html
  15. tinbucket

    How to fix warped plates

    If you use a slab roller and only roll the slab one direction, it can create uneven tension on the clay, and cause to shrink more in that direction. You may benefit by rolling the slab to the partial thickness, rotating the slab 90 degrees, then rolling to the finished thickness. You may also benefit from flipping the slab over. Another thing I have seen people do with slab plates is weigh them down while they are drying - a sand bag of sorts in the center of the plates. I think any combination of these techniques is worth trying. Some clays have a very sensitivd memory as others have mentioned and it is best to be aware of this when handling the clay - leatherhard pieces
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