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Ceramic Human

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    Ceramic Human reacted to Min in First glaze recipe attempt - looking for flaws and cone   
    Screen shot below of the UMF (unity molecular formula) of your glaze taken from your glazy link. 
    I've added some coloured arrows to try and help explain things. I don't know what you know so apologies if I've over simplified things, I'm just trying to give a general idea of what to look at while looking at a UMF. Very first thing I would look at when trying to determine the range the glaze will melt at would be the silica, alumina and boron levels. Fluxes always equal 1 with UMF, so look at the other things first.
    Having a look at the UMF below you can see the blue arrow is pointing at silica @ 3.18  (plus a bit from the zircopax which is zirconium plus silica) alumina (pink arrow) is 0.61  and  0 boron.
    Now comes the bit where you look at this and either compare those silica/alumina/boron levels with a glaze with similar qualities or at traditional "limits". There are differing opinions on limits, many interesting glazes fall outside these "limits" but use them as a guideline. For a durable cone 6 glaze alumina falls in approx the 0.25- 0.35 (Roy and Hesselberth) range and ^10 range approx 0.45 - 0.65 (Green and Cooper).  Now have at look at your alumina, 0.61  so this tells us a couple things, either this glaze won't melt well at cone 6 or it's going to be an alumina matte. (more on this in a bit)
    Silica in your glaze is 3.18, range for a durable cone 6 glaze is approx between 2.4 - 4.0 (Roy and Hesselberth) your 3.18 should be fine at cone 6, if the glaze melts well you want to get as much silica and alumina into it as you can for durability. ^10 range for silica 3.5 - 6.4 (Green and Cooper)
    Boron is 0 in your glaze. At cone 6 most glazes have boron to help the melt. ^6 range 0 - 0.3 (Roy and Hesselberth) for ^10 boron isn't necessary but can be used 0 - 0.255 (Green and Cooper). Bristol glazes use zinc as a flux but there isn't any of that in this glaze either so chances are it's not going to melt well.
    Red arrow is pointing to the fluxes in this glaze, sodium potassium and a fair bit of calcium. So back to the types of matte glazes, to get a matte glaze you can have high amounts of the fluxes calcium or magnesium or strontium or barium (not recommended) and to a lesser extent titanium and zinc. You can also have high alumina mattes but these tend to cutlery mark so not the best for functional surfaces. Green arrow is pointing at the silica:alumina ratio. At the 5.24 you can look at this and know it would be a high alumina matte plus have matting qualities from the high calcium level. (if the glaze melted at cone 6 which I don't think it will)
    Play around with the chemistry on Glazy,  get some boron in there, drop the alumina to a lower level, I'ld also raise the silica:alumina ratio up a little bit if you don't want cutlery marking. 
    Welcome to the land of rabbit holes.

  2. Like
    Ceramic Human reacted to neilestrick in Clay Disposal/Recycling   
    Recycling clay as an individual user is very different than recycling clay for a business or entire studio. The pillow case or plaster slab method doesn't work on a larger scale. For individuals it's great, though.
    I think there are smarter ways of getting rid of slop than piling it up next to a pond and killing vegetation. That is not a problem with the clay, it's a problem with the person.
    I also think that the clay pit mine itself is far more damaging to the environment that the small amount that I throw out. And you would be surprised at how much gets thrown out during production.
    I don't think there is a right or wrong answer to this. It all depends on your situation and what works for you. 
  3. Like
    Ceramic Human reacted to neilestrick in Clay Disposal/Recycling   
    I don't do any recycling at my studio. It's not worth the time and money. Lots of full time potters do not recycle, because their time is better spent making pots or doing other things related to running their business. Do not feel guilty about it. If you can donate it to someone who can use it, then do. But if not, it's just going to go back into the ground.
  4. Like
    Ceramic Human reacted to oldlady in Clay Disposal/Recycling   
    are you anywhere near a school that teaches ceramics?  consider donating if you have to do NO WORK  at all.
  5. Like
    Ceramic Human got a reaction from Rae Reich in Green Spots After Glaze Firing   
    Yeah, I thought about that and it's definitely possible, but I thought I'd ask you guys just to see if it was easy to rule out. There are so many factors, but I'm grateful to have this forum as a resource to help me get acquainted with the process.  Sometimes it makes my head spin. I don't want to be an out of touch manager.  The more information the better. 
  6. Like
    Ceramic Human reacted to liambesaw in Green Spots After Glaze Firing   
    You've been having issues with clay contamination, might be related?
  7. Like
    Ceramic Human reacted to JohnnyK in Green Spots After Glaze Firing   
    What tools do you use to mix the glaze? Is there a possibility that you might be using a tool that was used to mix the teal or green glazes that might have a miniscule amount of residue that sloughs off when you mix the eggshell. It sounds too simple , but when you're talking about .008% defects is it really something worth worrying about...unless you're like my wife who will spend 3 hours to find a one cent error in her checkbook balance?
  8. Like
    Ceramic Human reacted to Hulk in Green Spots After Glaze Firing   
    Hi again!
    Th' larger spot looks like an aggregation o' the smaller spots - looks like some o' the smaller spots are black, some green-ish; that true?
    Any road, suggest that you post recipes for glaze and clay, fired how, and how (and how often) glaze is sieved.
  9. Like
    Ceramic Human reacted to neilestrick in Green Spots After Glaze Firing   
    Crack one open right at the spot and see if it's coming up from the clay or if it's in the glaze.
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