Jump to content


  • Content count

  • Joined

  • Last visited

About Min

  • Rank
    Advanced Member

Profile Information

  • Gender
  • Location
  1. @ Kraythe, Last couple days you’ve had questions regarding low COE porcelain, low COE clear glaze, how to lower the COE of a tea dust glaze, replacing a frit and having a custom body mixed up. Bravo to you for asking so many questions, but….. With all due respect I think you need to slow down and listen to what Mark, Tyler, David, Neil,John and others are saying. They have a wealth of knowledge and experience. Ceramic work is not a sprint, it’s a marathon. I would respectfully suggest you take the time you need to either try out a bunch of clays and test the heck out of them before committing time to making a whole whack of pots or test the clay you already have and see if the glaze COE does have to be as low as you think it does. Plainsman Clay up here in Canada doesn’t publish COE figures, Georgies in OR, Seattle Pottery Supply and Tacoma ClayArt in WA don’t either. I really wouldn’t get too hung up on only trying clays that supply the COE data. Try a bunch, put your glazes on them and see what happens. If you LOVE the clay you currently use then try out some (fully melted gloss) glazes with different COE’s and see what happens.
  2. Yes, it's Cone 6, since yours was I figured that's what you were looking for. Your recipe COE is 5.8, mine is 5.7 that's a very tiny difference. Play around with the recipe, you can supply the boron with a number of frits or GB substitutes like Gillespie Borate etc, see what you have in your studio and work it in. If I can make a suggestion, start with supplying the boron then go to the fluxes, balance the alumina and silica last. If you want to supply the MgO with magnesium carb then sure try that. More than one material can supply the necessary oxides, play with what you have.
  3. Plunk this in to your program and see how it compares. The MgO won't be as fluid as it's not fritted but I use a very close version of this and it works for me. Wollastonite 5.70 EP Kaolin 23.70 Talc 3.30 Silica 32.80 Minspar 12.60 Gerstley Borate 19.50 Dolomite 2.40 100.00 edit: this is a low expansion glaze, it will likely shiver and or dunt on typical stoneware bodies. Due diligence needed to test for this. COE can be raised if necessary.
  4. Mason Stain in base glazes

    Hi Ron, The large amount of RIO in the Licorice Black glaze recipe has an effect to reduce crazing, as does the cobalt. I would suggest not including colouring oxides in your COE figures, click "phantom" with your Insight program next to them so they are not included in the math and see what the COE comes out as. Yup stains change the COE, 6600 has cobalt, chrome, iron and nickel, thing is we can't find out the proportions of each so back to trial and error testing. What you don't want to do is put a high expansion glaze on the outside of a pot and a low one on the inside (or vice versa) as this can lead to dunting.
  5. sorry, I was vague. Look at the pictures of the two recipes you posted for VC's Teadust. Have a look at the Si:Al ratio that is on the right side of each picture. Original has 8 point4 : 1, now look at your altered glaze, the ratio is 16 point 5 :1 What this is telling you is a couple things, how the glaze will melt and therefore the gloss of it. Have a look at what Custer has in it, the main fluxes are sodium and potassium When you removed those you lowered the COE, good start. But you need to replace those fluxes with lower COE ones and yet not change the quality of the glaze. So, to replace high COE fluxes (or just part of them) you need to bring in low COE ones. Magnesium and lithia are good places to start. You already have some magnesium in the glaze (from the talc), that would be one place to start increasing it. I would also add some spodumene but don't go crazy with how much you add. Could also play with the calcium level, probably could lower that a bit also. Sometimes it's easier to think in terms of cooking. If you have a brownie recipe with lots of fat and you want to make a lower fat recipe what would you do? Take out some of the butter right? But if you do that alone you will have nasty dry brownies so you need to replace it with something. Applesauce instead of all or some of the butter will reduce the calories and yet the brownies will still be brownies. make sense? To look at mole percentage instead of a unity formula with Insight look in the lower left area of the screen and under "Calculation Type" click the button and scroll through to Mole% then on the right side of the screen click the box with the red X and it will take you to a list of choices of Targets and click "Eppler Cone 6" or whatever cone you are firing to.
  6. pssst look at your silica to alumina ratio
  7. Unfortunately no, you can't do this but you can figure it out. Make up a series of clear glazes with COE/CTE figures ranging from very low to high. Don't add any opacifiers or colourants to them. Fire them same way you fire your pots then do stress testing to test for crazing and shivering/dunting for the low coe ones. You can see what the range of COE's will be that will be craze free and yet not so low that they shiver or dunt. What does complicate things is that the combination of fluxes used will have an effect on crazing or not but the clear glazes test will get you most of the way to figuring it out. Example of this would be zinc oxide, it can actually decrease crazing in some recipes and yet with glaze calc it looks to raise the COE. (pm me if you want my list of clears with increasing COE figures) When you look at COE figures for any given glaze don't include opacifiers or colourants. Many can look like they are increasing the COE figures but in fact the crazing will actually be reduced. Zircopax would be an example of the former and titania from rutile or titanium dioxide examples of the latter. My porcelain plus a red clay I use have COE's below 5, it's doable to make the low COE glazes craze free but it does take a lot of work and like Neil said not all can be lowered without drastically changing the qualities of the glaze.
  8. Mason Stain in base glazes

    I use 2 of those stains, depending on how intense you want the colour but around 7-10% of the 6600 works to get black. It's an expensive way to get a black glaze though, the Licorice glaze from the same book using 2 cobalt carb and 9 iron makes a nice solid black. I make a pale yellow with 1 point 25 of 6464. The chrome green stains can be really intense, I would start at 0 point5% and test up to 3 point 5% at the very most. Easy way to test amounts would be to mix up 100 base plus minimum amount of stain you think you need (like 6 for the 6600) dip a test tile. Then add another 1 gram of 6600 and dip another tile and so on up to say 10 for the 6600. Not super accurate as the glaze quantity decreases with each subsequent dip but it will get you close. For strong stains or very pale tints go up by fractions of a percentage.
  9. How to mix Dry Glazes Safely

    After weighing the dry ingredients into the bucket slowly add about 70% of the water you will need then put a lid on the bucket and let it slake. After the ingredients are wetted then mix it up and adjust the water content. Don't dry mix or if you really have to put the materials in a tightly sealed container, mix it up then leave it so the dust settles inside. An immersion blender for small amounts of glaze or jiffy mixers on a drill, a wooden paddle etc all work well. P100 face mask, wipe down the surfaces afterwards and if possible ventilate the garage.
  10. Genesis Controller

    I've been using one since about January of this year. It's very user friendly, no issues with it whatsoever. Think it's well worth the extra bucks to upgrade to it.
  11. Homemade Underglaze Trouble

    The recipe below is from George Vardy, he is the tech consultant at Mason stains. If you try it really don't skip the VeegumT (I've used macaloid and it works too). Chrome greens can need extra flux to melt, calcium carb works. EPK Kaolin 10 parts Feldspar. 25 parts (I used custer) Flint. 25 parts Stain. 40 parts Mix well with water, add 1 part VeeGum T that has been FULLY broken down in water, screen through a 100 or finer screen, bring to your painting consistency by addition of more water if needed. When using very strong stains such as cobalt blues or chrome greens you may need to reduce the amount of stain if the fired color is too strong for your requirements. This can be used to decorate on clay or bisque. Be sure to dry fully before glazing. Is it bloating in the clay or something else? Body bloating can be caused by organics in the clay not having sufficient time to burn out in the bisque or overfiring and the clay starts to break down and gas off causing the bloats. Are there bloats on the parts of pots without the underglaze or glaze that is giving you problems?
  12. 1 4 3 1 (but I thought Mr Dean nailed it so???)
  13. This is what I take those terms to mean. Soak: keeping the kiln at any given temperature for a set length of time. Example: at the top end of the firing, holding the kiln at the final temperature to mature the glazes/clay. Can soak at any temp going up or down. Hold: I take this as pretty much the same as a soak. Can hold at any temp, example would be crystalline glazes needing an extended hold on the temp as the temperature declines. On single thermocouple kilns or manual kilns a hold or soak helps even out the temperature in the kiln. Candling: Warming the kiln and pots slowly and keeping it a low temp to thoroughly dry the clay. I’m guessing this term came from combustion fired kilns and there literally was a flame. Preheat: Warming the pots up but not necessarily holding the temp as with a candling. Example would be when raku pots are put on top of the hot kiln to get them warmed up a bit prior to firing.
  14. Kind of a backwards answer to the question, for people who say don't eat at a show, I really can't do that. It takes a lot of energy out of me doing shows so I pack healthy easy to eat and drink food to take with me. Easy to eat stuff like almonds, grapes, protein bars, small cartons of milk, bottled water, pouches of squeezable food etc. I don’t rely on buying lunch from the show. If I don’t eat during the day I tend to just stuff my face with junk food after the show and then regret that later. edit: just remembered what my neighbour during my summer markets does, text, text, text. Looks like she doesn't really want to be there.
  15. The truth about crazing

    Thanks for posting the info re how much crazed glaze weakens a claybody. It corroborates other data I have read regarding this. I'm guessing the finer the craze pattern the weaker the claybody? Or would the thickness of the crazed glaze be more of a factor? Agree that adding silica and kaolin will work in cases where the base glaze can take the amount needed to fix the crazing and yet still melt properly. When that fix alone doesn’t do it I find swapping out some of the higher expansion fluxes, while keeping the silica:alumina ratio constant, for ones with a lower expansion will usually get you there. Yes, there can be colour shifts with alternate fluxes but just talking crazing here. The combination of fluxes used doesn’t always represent an accurate coe/cte figure as some fluxes have a symbiotic relationship with others in regards to lowering the crazing while the coe figure might still be higher than a target one size fits all coe for any given clay. (referring to fully melted gloss glazes here, not mattes)