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Min

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Everything posted by Min

  1. Re the debate of a refractory underglaze or not it would be fairly simple to test this theory without altering glaze recipes. Since we know adding flux will make things less refractory and adding alumina the opposite, using this logic I'ld run 2 parallel tests, one adding flux, Gerstley Borate should be a good choice, and the other adding calcined kaolin. Say roughly 1 Tablespoon liquid underglaze + 3/4 teaspoon of Gerstley Borate or calcined kaolin plus enough additional water to make them brushable. Apply to both a vertical and horizontal surface with the same number of coats and fire them both the same and see what comes out of the kiln.
  2. Lovely that you found a solution that works for the potters in your studio but from reading the original post from @carolrossit sounds like she is using a commercial brushing glaze. I think we need to work within the parameters of the the op's usage insofar as commercial versus studio mixed glaze. Like many things in ceramics there are times we can make things more complicated than they need to be.
  3. A potash feldspar? What boron frits do you have? edit: have you tried other iron saturates without boron?
  4. Before doing more work I'ld run some tests with thickness / number of layers. 5 coats seems excessive. Have you tried Spectrum Black 515? I use it watered down and 2-3 fairly thin coats for solid coverage. (it's on the bowl below) If there is dust on your pots if possible try using compressed air to blow it off before glazing if you don't need to wet the bisque. This might be another thing to test, unwashed, wiped with a clean sponge, compressed air, dipped in water etc. EDIT: I'm going to edit the title of this thread to better reflect it's contents. Going forward it will make it easier to find it when doing a search.
  5. If I was starting over again that's where I would put the money.
  6. - Cobalt will make a purple to purplish to bluish colour with magnesium but the magnesium level needs to be quite high to really get the purple tones. I don't think 3% magnesium carbonate will get it high enough. If you are glaze testing anyways you might as well try it, I'ld try 0.2 up to 0.5 cobalt carb. Just do a progression blend, they are fast. - Chrome + tin can make pink if the base glaze is very high in calcium. These glazes typically are also on the low side with magnesium and alumina. For doing test batches a really accurate scale is necessary, especially for the chrome. If you just want a general idea if this base glaze will work then skip the blends and just try 0.20 chrome oxide + 6.0 tin oxide and if you get a red tone you will know if this base supports chrome:tin pinks / reds. If you get pink / red then work on the cobalt to shift the colour. - I would also try it as is with the manganese dioxide. Pinks can be made with high alumina glazes + manganese. - You can get pinks from rutile, with and without tin but it's easier to supply the chrome from chrome oxide rather than the trace amount in rutile. - If you do try the chrome / tin be aware that having chrome in the kiln can flash nearby pots containing tin to pink. - How much of this glaze did you mix up? Is it in liquid form now? Welcome to the forum
  7. The point that bothered me the most was equating "embracing a mistake" with being handmade and unique.
  8. In @Magnolia Mud Research 's post he found 10 - 12% the sweet spot. Perhaps what is needed for concrete retardant isn't the same requirements for changing the crystal structure for the agglomeration issue of wollastonite. Interesting for sure, it would also be interesting to test different slaking times. Perhaps less sugar could be used if slaking period was longer.
  9. I'm getting different math using Callies best result figures of 20 grams wollastonite + 2.5 grams of sugar. I think you are using the higher amount of sugar figures that didn't work as well? 20 grams of wollastonite + 2.5 grams of sugar, multiply the 20 grams by 5 to bring it up to 100. Multiply the 2.5 grams by the same amount (5) brings it up to 12.5 So for each 100 grams of wollastonite it would be 12.5 grams of sugar. Therefore 500 grams of wollastonite would require 5 X 12.5 which would equal 62.5 grams. Using your Googlefu weight of one tablespoon weighing 12.5 grams that would be 5 tablespoons sugar per 500 grams of wollastonite. It's late and I could have messed this up so double check my math.
  10. Agreed that for volume glaze mixing a rotary sieve is great, be it a Talisman or using a slow speed drill with a brush attachment but I haven't found it helps with the wollastonite issue. Gritty bits of it get stuck between the bristles and around the edge of the mesh that still need working through the sieve with a bit of water and a spatula or some such thing.
  11. I guess where on the continuum you are looking at things from makes it old or new school? New school isn't really new any more for kiln controllers but they have gotten more bells and whistles since the first ones came out. I'm new school there I guess, I love my Genesis controller. Glaze calculation software, is that new school, I'm not sure but it beats the old pencil and paper way of doing calculations. Silicone ribs, maybe those are new school? Clay in boxes, new school? Can't imagine processing my clay from the ground like in the old Isac Button videos. Combination mixer pugger, yup, I'll tick that box too, relatively new school there for studio potters. Electric drill with a mixer attachment vs the old wooden stick to mix up glazes. Using the internet to connect with other potters, is that new school? Reading books, old school I guess but nothing better. Paper and pencil note taking just in case my computer crashes and I loose all my notes because I'm bad at backing things up and not everything is stored in the cloud, old school. I guess I try and take the best from both ends of the spectrum.
  12. If you take out the frit I would add some feldspar, preferably a potash feldspar like custer. If it comes out too matte then add a titch of frit also. Experiment with the thickness of the glaze also. Ash glazes are typically used on the outside of pots and a liner glaze used inside. Ash glazes are typically low in silica and alumina. Have a look at the article by Harry Spring in this link, might be useful.
  13. What process are you using to dial this glaze in? Line blend or ? There aren't a lot of cone 6 ash recipes published, one that has been around for a while is Frasca Ash ^6. Don't know if you've come across it, link here if not. Note how it's really high in ash, as is your recipe but it also includes whiting. It also uses ball clay instead of kaolin, this could be helpful as ball clays are "stickier" so if you have a soft glaze laydown using ball instead of kaolin will help. Regarding the rough rims, often people will glaze a pot with a base glaze then apply the ash glaze to the upper areas of the pot and allow it to run down the pot. Having a stable base layer glaze will help it from running off the rim. If you try that recipe or adjust yours to something similar it's still very much dependent on the chemistry of the ash you are using and that is going to be different with every batch of ash. This is where doing a line blend could be very useful. I've seen cone 10 ash glaze recipes with under 20% ash, they are using a larger proportion of whiting plus some dolomite to get the rivulets / stringers effect. Even taking an existing glaze you have and doing a progression blend of it plus a blend of ash + whiting should get you some ash effects.
  14. Hi Carmela and welcome to the forum! The title is what you entered first then in the body of the post (where you wrote "Not sure what I need to put here.") is where your comment or questions would go. It's fine as it is but if you want to edit it that would be fine too. If you need help or have questions with editing just ask myself or any of the mods.
  15. Thanks Lou, interesting stuff. So it's the hydration aspect that comes into play with sugar then? I was wondering about the flocculation that you had with your experiment so I googled sugar + flocculant and it turns out there is a flocculant added to cane sugar processing, I'm taking one of your SWAG's and thinking that is going to have a minimal effect on flocculation though, if indeed it ever was used in the sugar you used.
  16. @Magnolia Mud Research, what type of calcium silicate were you working with?
  17. I don't recall that wollastonite is especially hygroscopic, at least not to the point that zinc oxide is. Wollastonite has a needle like crystal structure that causes clumping. Stick your hand in a bin of wollastonite and grab a handful with your fingers pointing downwards. It won't flow out of your hand the way other materials do. It's almost like the wollastonite has loosely velcroed / clumped itself together.
  18. Wollastonite agglomeration is a nuisance for me too. I find the older my supply is the worse it gets so I just buy a single 50lb bag at a time. Only thing I've found that cuts down on sieving time is whizzing it in a blender (with some of the glaze mixing water) does help. My main glazes have about 15% of it, takes a few batches to get it all whizzed up and scrape out the blender but saves sieving time in the long run. Even so I usually have a teaspoon or so left in the sieve (I use 80 mesh) so I have gotten in the habit of just adding an extra little bit when I weigh it out. It would be good to hear if anyone has a faster solution.
  19. Glazy gives you prompts when typing a recipe in. I just tried it using "Red" and the options that came up were Red Iron Oxide, Red Clay, Redart and Newman Red Clay. I then tried typing in Red Copper Oxide and the prompt/option that came up was Black Copper Oxide. There is an info page for Red Copper Oxide on Glazy though. Lots of versions of this glaze, I've never seen one that uses any form of copper, it's always iron so my thought is it should be Red Iron Oxide.
  20. Yup, it will be fine. You could cut it back by about 1/3 since the hydrate contains more water but not necessary for your purpose.
  21. Trying to broaden this question out to include more than LOI as a possible culprit for pinholes. It's been my experience that pinholes can be caused by a number of things. Since one glaze high in calcium carbonate won't have a pinhole issue and another will there are other factors in play. A few things that I've found contribute to pinholes from bisque to glaze fire. Groggy claybodies more prone than smooth or porcelain claybodies. Clean bisque firing necessary to fire out organics etc from clay to prevent claybody gasses being expelled through the glaze. Glaze application. Dampen the bisque ware if necessary to help prevent air bubbles escaping from the bisque, especially on trimmed groggy bodies. Raw glaze thickness, avoiding too thin a glaze application or overly thick and also glaze laydown. Under or over firing the glaze. Fire the clay to its maturity and adjust the glaze if necessary. High viscosity glaze recipes have a more difficult time healing over the pinholes during the firing, fluid glazes not really an issue. Large amounts of LOI materials such as dolomite, calcium carbonate, zinc, rutile in a viscous / low fluidity glaze. Drop and soak/hold firing helpful in clearing pinholes.
  22. @rawtoast, have you tried just emailing her and asking?
  23. @thiamant, I started a new thread concerning pinholes using your last post as the lead. This thread has evolved into one concerning pinholes rather than the op's original issue. New thread here. https://community.ceramicartsdaily.org/topic/26118-glaze-pinhole-causes-and-remedies/
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