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Min

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  1. I've moved the above post over to this new thread since we had gone quite a bit off topic. Discussion the above post is from is this one. https://community.ceramicartsdaily.org/topic/26100-does-frit-3124-bubbles/
  2. Had a look at some of those test tiles from Glazy using this recipe. I'm seeing pinholes in the red clay one for sure and smaller pinholes and semi healed pinholes in others, couple examples below. Pins on the red clay could also be from offgassing of the body. Agreed that mixing the recipe with the appropriate frit is important.
  3. The op is using approx 22% of a boron frit. Boron frits melt early. From your posts on this forum I believe you are firing to cone 10 and your glazes do not contain boron. Cone 10 glazes contain materials that get taken into the melt later in the firing than lowfire or midfire glazes. If you have ever had the misfortune of having to stop a firing part way through because of a power or kiln issue and open the kiln you will probably see partially fused glazes well below the firing peak temperature, particularly with fritted boron glazes. Melt fluidity article here that starts getting into this. How glazes melt article here that goes through the glaze melt process. There is also the article discussing the importance of looking at LOI from Peter's chart above with which he included a link.
  4. Think of wollastonite as natures frit of silica and calcium which can be taken into the melt easier than a chemically equivalent mixture of silica and calcium carbonate and has a far lower LOI. Boron frits such as Ferro 3124 are starting to melt by 760C. Calcium carbonate decomposes between 750C - 1000C, so the frit is definitely going to be melting prior to the calcium carbonate being finished off gassing. Since it has one of the highest loss on ignition of all the materials we use it just makes sense to supply the calcium from wollastonite rather than calcium carbonate when there is a significant amount of calcium required for the recipe as is the case with this glaze recipe. Perhaps, kind of impossible to know for sure though, especially since we don't know how "dirty" the op's claybody is. When people have just re bisque fired dark bodies with a typical schedule to clean out more of the problem inorganics, organics and sulphur it isn't necessarily successful. It takes slowing down between 700 - 900C range to allow time for the inorganic carbons to burn out.
  5. A few thoughts about what could be going on with this glaze. Two of the main ingredients, the 3124 frit and the nepheline syenite both begin melting at low temperatures. What this means is any gasses that didn't get fired out during the bisque can get trapped when the glaze starts to melt which seals off the surface of the claybody not allowing any remaining gasses to escape. When the gasses can't escape through the glaze surface they can cause the blisters/bubbles like you are experiencing. Do you vent the kiln well during bisque firing? What's your bisque schedule? Second thought is you might be firing way too hot. 130C / hr / 1235C peak plus a 20 minute soak could very well be putting you in the cone 7 - 71/2 range. Are you using cones to verify what the kiln is actually getting to? Overfiring can also cause blisters/bubbles. Third thought after looking at the glaze recipe is there is a lot of raw kaolin and also whiting in the recipe. That much raw kaolin (epk) could very well lead to a crawling glaze. Also, if you have access to wollastonite I would supply the calcium from that instead of the whiting. This will reduce off gassing and the glaze will also melt better. I redid it, using part calcined kaolin and wollastonite below if you are interested. Being in Taiwan we don't know the chemistry of your materials but this should get you in the ballpark for this high alumina matte.
  6. I wonder if you could use red iron oxide + water + a food safe gum to thicken it so it doesn't just run off and make a big mess. Brush on the fish, do the print then wash it off. Welcome to the forum.
  7. Just a heads up to anyone who might substitute Sierralite talc for Amtalc-C98, there is a significant difference in chemistries between the two talcs. A direct 1:1 substitute likely won't work unless it's just a very tiny amount of talc being used. Main differences are in the silica and alumina levels.
  8. Sounds like Callie's third party insurance would be something to look into. Thanks for getting the word out about UPS and lack of accountability for insured lost packages containing ceramics and null and void issue when shipped without their pre-approval documentation.
  9. If all else fails it sounds like good therapy.
  10. No for glaze fires but I would consider bisque firing if I knew the person and they were okay with my ^05 bisque firing schedule for white claybodies. Probably not a huge demand for bisque only so it's probably a moot point.
  11. Change the materials (like the spar or nepheline syenite etc) and you will get a different COE that fits or doesn't. COE figures work best when the materials don't change but the amounts of them can. 6.5 might fit for one glaze recipe but not another that uses different materials due to a number of factors such as oxide elasticity, excess oxides, oxides that don't expand in a linear fashion etc. edit: @thiamant demonstrated this when they decreased silica in some of the tests: "....and tried with different silica levels, decreasing silica levels really makes things worse ( I was hoping maybe less cloudiness by doing so, but all tests from 1 to 4 had crazing)"
  12. My sister is an engineer and I have a friend whose husband is a nurse, thank goodness we have evolved from those misogynistic attitudes and gender stereotyping.
  13. An easy way to do this is just type in Google 6,000 + 3% and Google will give you the answer of 6180 You know 6,000 is the total of the base glaze so the difference of 180 is the colourant amount. (6180 - 6000 = 180) For your blue stain Google 500 + 0.7% and you will get the answer 503.5 Now subtract your base of 500 and you have your answer of 3.5 Works with any oddball number you can think of, don't have to work in multiples of 100.
  14. 0.07 is going to between 0 and 0.10 (it's going to be an absolutely tiny amount) 500 grams will need 5 X 0.07 which will be 0.35 0.35 is going to be roughly a third the way between 0 and 1.0 on your scale (still a really tiny amount for 500 grams of base) Are you sure it wasn't 0.7 of cobalt or stain? If it is then you would need 5 X 0.70 which will be 3.5 grams for a 500 gram batch. Make sense?
  15. Have a look at cone 6 ash glaze formulas. One below to have a look at plus a popular fake ash recipe. Have a look at the SiO2 and Al2O3 levels. Granted ash figures are going to vary widely dependent on the ash used but it gives you a general idea of the chemistry. To get the runny rivulet property of an ash glaze it will to be fluxed with calcium and have low alumina. The Hanna's Fake Ash has higher alumina levels but still are low. Granted some silica and alumina could be pulled from the body but ash glazes are traditionally used on the outside of pots for decorative use. Just to make it easier a limit's chart also. Many of the really interesting glazes with visual texture come from glazes outside the "limits".
  16. I get updates from a few ceramic supply places. Have heard from a couple of them that there is going to be an increase of up to several hundred dollars coming on August 22, 2021 for Skutt kilns. Don't know if anyone is considering a new kiln but it might be time to act quickly if you are. Double check with your own supplier.
  17. If you cover up all but one of the shapes the clay is going to come shooting out of the pugger way too fast. It will be an awful lot of pressure for just one small extrusion. When I put a handle die on my Bailey I put the cutout shape at the top of the die so the extrusion is laying on top of the others then lifted it off and scrapped all the other shapes after it was pugged and tossed the unwanted ones back in the machine. You could try a partial blockage but there isn't really any point doing it. For my electric extruder I block off areas with expired gift or credit cards, could do something similar, just put the card(s) between the clay and the die.
  18. Might want to try lowering the KNaO2 even more. Along the lines of 0.15 LiO2 and 0.11 or 0.10 KNaO2. Since you are firing tests anyways do a few of them to save firing more than you need to. Lithia could be bumped up to 0.20 I would also suggest dipping / spraying different thicknesses of glaze, might be able to really thin it down which will likely make a difference with the clarity of the glazes. I'ld also add your materials into the Eutectics Calculator and see if the glazes are oversupplied in some of the fluxes. That calculator is new here, if you can't enter your spar and nepheline syenite you could DM @BobMagnuson and ask him about it.
  19. Plus to avoid the opposite, shivering. I believe there are 3 main methods of measuring an oxides COE / CTE, they all measure a sample during a thermal cycle. Ceramic oxides, like most substances, expand when heated and contract when cooled, this is what is being measured.
  20. It's my understanding that UPS covers for loss and damage for fragile items, including ceramics, only if the items goes with their "Pack & Ship" method of shipping. If you pack it yourself it isn't covered for damage. If the parcels are lost then it seems strange you can't file a loss for them, regardless of what is inside the parcels. Perhaps it's a different policy in the U.S.
  21. You just pointed out one of the parameters of using (reversible) COE or CTE figures. They do have their limitations, first off the glaze mustn't be crystalline; it must be fully melted. Other factors that need to be taken into consideration are glaze elasticity, oxides that don't move in a linear fashion such as lithium and boron and while comparing formulas the same oxides need to be present in the ones being compared. If you want to test this increase the Nefelina Sienita Prodesco content of your glaze and see if the crazing doesn't get worse. (while balancing the silica and alumina) A simple and sometimes effective way to solve crazing is to add silica and alumina, this will work if and only if the glaze will melt enough to incorporate the additions. Not to keep banging on about it but the glaze must be a fully melted gloss glaze to utilize COE figures. However by understanding the properties of the oxides we can utilize the low versus high or somewhere in between information for claybodies and matte glazes also. Example of this is the stovetop cookware that utilizes spodumene or petalite. Plunk the figures into a glaze calc program for one of these claybodies and it will give you a COE figure but it's not applicable since the clay is a crystalline structure not a fully melted homogenous matrix and yet we know a flux containing lithia is often used in very low expansion stovetop claybodies. COE is measuring the reversible volume of change of a ceramic oxide when heated and cooled back down. This is relevant since that is what our glazes undergo. Using measured COE figures is another tool in the tool box and like all tools needs to be used appropriately. We know what the COE of the oxides we use are (given they could be slightly different depending on source). On the high end of the expansion oxides we are looking at sodium and potassium and on the low end we are looking at lithium, magnesium, silica and alumina. @BobMagnuson has permitted this forum to have access to his Eutectics Calculator. I entered the original G1947U glaze into it. Very slight oversupply of slica (1.43) and alumina (0.02). If you are questioning an oversupply of an oxide it's a great tool to utilize. (link at the top of this section)
  22. I had a quick look at your Feldespato potásico extra that you used in place of Custer feldspar, there are enough differences in the sodium and potassium that just might make a difference in the melt. Your Nefelina Sienita Prodesco also is a bit different, both mostly in the sodium and potassium levels. I'ld do a side by side comparison of both recipes using your ingredients compared to North American. Custer Feldspar and Nepheline Syenite A270 and look for differences. Other thing I noticed is you didn't rebalance the calcium in your Nefelina Sienita Prodesco version. Screenshot from Glazy of you Grolleg + feldspar on left compared to the Nefelina Sienita Prodesco. Calcium is one of the higher expansion oxides, dropping that down will reduce crazing but I'm not sure it's enough to eliminate it. If you go with the Neph Sy version (using your Spanish material) I'ld go for about 1/2 that and 1/2 spodumene to bring the expansion down. It will probably put the flux ratio in the 3:7 range but should still be a durable glaze. I'ld also try the original or grolleg version again and just thin it down some more. Easiest fix would be if a thinner layer is all it takes. Take the sg down to about 1.3 and just do a quick dip, see if that does it. Might find the same problems using Marks version of this glaze since it's pretty much the same glaze but with a higher loss on ignition and a tiny bit more iron.
  23. If you remove the zinc from Marks recipe it is virtually the same formula (molecular) as the 1947U. Screenshot below. Wollastonite to supply the calcium (in place of whiting) and ball instead of kaolin. Makes me think that either might work if it was fired hotter. I'm guessing the 1947 was based on the same recipe Mark uses. Likely because it's lower in sodium. I've got to get some work done here but I can look at your spod version later today if someone else doesn't do it before me. If you post the spodumene recipe you are thinking about it will be faster. It's good to know you aren't getting crazing with the g1947u. Are you verifying you are getting to cone 10 with witness cones? Underfiring could account for both the crazing and the cloudy look.
  24. I don't think the simple fix of adding silica will fix the top glaze. It's hard to clearly see how much crazing is in the second one with zinc. Do you have any Spodumene or Petalite? Lithium carb? Are you getting to a full cone 10? Checking with witness cones?
  25. This isn't how I would look at this. What you have found out is that over time those clears would likely craze using those ingredients in those proportions. Better to find that out now rather than after you made a bunch of work with it. Making a well fitting crystal clear glaze is one of the harder things to do and does take some work. When you add another ingredient (like zinc) the COE figures don't go in a linear fashion from one glaze to another without it. COE figures are good for comparing glazes when ingredients don't change but not necessarily between glazes using different materials. It's like adding a new family member to the home, the dynamics change. Have a read through this thread on crazing with 1247U cone 10 clear and the solution the op came up with. Just a note, the fellow who was testing the low expansion clears in the thread I linked to eventually found out there was an issue with the manufacture of his claybody. Like all good dialogues there is some back and forth on methodology. ( I favour reducing high expansion fluxes for lower ones when the crazing is more than slight) edit: how far apart are your craze lines?
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