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About Min

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  1. 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)
  2. (cough, cough, cough, Aug 09th email...) One of my kilns doesn't have protection tubes (ConeArt) I use one of those synthetic dusters and gently brush the tips before glaze firing. Not my idea (or kiln) but this might help
  3. This one is really fried. I've had a few that get a crack through the welded tip way before they get as burned out as this one. Anybody have any data on K type TC's 8 gauge or 14 gauge, which lasts longer or if the gauge irrelevant? Joseph, the temp reading can drift when the TC starts to go, weld gets weak and doesn't read properly. I wouldn't let yours get as fried as this one. It's a (relatively) cheap thing to fix.
  4. Another clear glaze question

    Did you get the PM with the recipes I sent yesterday?
  5. Strange brown specks !

    Just as an aside, 200C / 390F is awfully hot to be candleing at. (around 85C / 185F and up to 93C / 200F works for me)
  6. 4 3 2 (changed from 3) 3 don't know if the "rules" of this PQotW allow me to change my answer to one of the questions? If I can I'm changing the answer to #3 to 2 claybody being used.
  7. firing schedule needed

    I would just run the candle overnight then if you have 4 ramps the Bartlett controller slow bisque program should work. candle: get the kiln up to 185F over 2 or 3 hours then once it's there hold at 185F overnight. Then I would enter the slow bisque profile from Bartlett controllers: 200F an hour up to 1000F 100F an hour up to 1100F 180F an hour up to 1676F 80F an hour up to end of firing temp (I don’t know what you fire to, ^04 would be 1926F with this program)
  8. Help me diagnose this problem?

    If you find one of the blends work then just combine the two recipes in the appropriate ratios. So, if #3 works you would combine 66.6 Glaze A with 33.3 of Glaze B in a new recipe to total 100. (glaze calc programs can do this super fast) You could change the ratios to 10:0, 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, 1:9, 0:10 or any combination you like. hmmmm, I just looked up that Standard 551 and they list the absorption at 0 point 3 so it really shouldn't leak. Glaze should not be relied upon to seal a claybody. I used to think that also but it doesn't work that way. Pinholes, crazing, micro fissures in the glaze are going to let water through. For functional pots that will contain liquids the clay without any glaze should not leak. I would run the tests that were outlined in that other thread I posted and measure what the absorption is with your firing methods. Something screwy going on if you are getting leaking with this clay fired to maturity.
  9. Help me diagnose this problem?

    The more you edge toward a dry stony matte the more cutlery marking you will get. Stony mattes are fine on the outside of pots if cutlery marking is an issue. For surfaces that will be used for cutlery a glaze that has more gloss will mark less. You need to find a balance between the two that works. Basically if you take a clear glaze and do a glaze line blend with it and your matte you should find the sweet spot where it is no marking and yet isn’t a gloss either. If you haven’t done one before a line blend is super easy to do and gives you a bunch of test samples with just 2 glazes. In the chart below A would be your dry matte glaze and B a clear gloss. You would weigh out 200 grams of dry base for each and add the exact same amount of water to both. Then use a teaspoon, tablespoon, syringe, whatever, to scoop out the parts of each glaze to blend together. For example #4 would be 3 parts of matte plus 3 parts of gloss. The #1 and #7 are the control base glazes. Glaze and fire the test tiles the same as your pots are fired. After doing this test you can then fine tune it if needed. (I like the G2934 matte from this page.) Re leaking, this has come up here a fair bit lately. If your clay is either under fired or has a high absorption rate it will likely leak. As you are using porcelain it should be nice and tight and not doing that. What clay are you using? Hopefully it's not a wide firing range one. Also, are witness cones used to verify firing? There is more on absorption here. I just plunked your recipe into Insight, calcium and magnesium are not high enough to be matte from those and I don't think the alumina is high enough for a stony alumina matte so it leaves me thinking it is matte because it is underfired.
  10. Good Slip

    There are a number of them here. There is a Randy Brodnax ^6 ox or reduction black in there. For a work around not using Mn, I would play with cobalt, iron, chrome amounts. (chrome if flashing won't be a problem with tin opacified glazes)
  11. The Crafted Dish

    you are sooooo Canadian, leaving your entry as the last line
  12. but can you use the chicken cup as a frisbee?
  13. Bad Habits with Manganese

    If you are loosing sleep over it then you could always request some blood work be done to test for Mn.
  14. Can I save this mug?

    Like everyone else is saying, hammer time. Except, first I would probably put them in the sink and fill them with boiling water, think the crack might then go right through the wall. Be an interesting experiment. It's really hard to tell by the picture but is there (thin) glaze going over the edges of the crack? If there is then the crack could be from a bisque dunt and was there before you glazed them. They can be really hard to see but smooth edges on a crack usually means it was there when the kiln fired up not down.
  15. Raku Proposal For School

    If you do smokeless then great and obviously that would be the way to go. I think it was the fumes from the copper that made me so sick, still can’t take the smell of raku without it triggering a nauseous feeling. Used sand beds and wet blankets over the bins, perhaps some people are just more sensitive. To the original question, if you are going to use one I would just use the same respirator you would use for mixing glazes, a P100 like this one.