PottaFella Posted November 18, 2016 Report Share Posted November 18, 2016 Been using a Michael Bailey Cone 6 recipe 'T14' that is now very badly crazing on a stoneware body ES5 (image attached - illustrated jug) which I actually fired to more like cone 8. I modified the glaze slightly in that it did not contain the Lithium carbonate given in recipe. No crazing that I noticed when it came out of kiln, but over several weeks it has been getting bad. Main problem – the jug leaks! As far as I can remember I did things 'right' ie. nice slow cool down and didn't open the kiln until temp was quite cool. Had been previously bisqued at 1000c. Please do take a look at recipe below and can anyone say if it looks likely to craze, 'cause if so I will look for a more reliable glaze. Soda feldspar 70 Bentonite 3 Lithium Carb 3 Dolomite 7 Zinc oxide 5 Flint (or quartz) 12 Many thanks for any help Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted November 18, 2016 Report Share Posted November 18, 2016 It does probably have quite high expansion with all the soda feldspar. Lithium will help the crazing. If you have no lithium carbonate you could swap out say 5 of the soda feldspar for a lithium feldspar (if you have that) and see if it fixes the crazing. Is it leaking out through the bottom? Could be that the clay is underfired even at cone8. Usual rubbish from the company that "Scarva Earthstone Original White matures between 1180°C-1280°C" Link to comment Share on other sites More sharing options...
neilestrick Posted November 18, 2016 Report Share Posted November 18, 2016 The lithium will have a big effect on the COE of the glaze. Link to comment Share on other sites More sharing options...
PottaFella Posted November 18, 2016 Author Report Share Posted November 18, 2016 It does probably have quite high expansion with all the soda feldspar. Lithium will help the crazing. If you have no lithium carbonate you could swap out say 5 of the soda feldspar for a lithium feldspar (if you have that) and see if it fixes the crazing. Is it leaking out through the bottom? Could be that the clay is underfired even at cone8. Usual rubbish from the company that "Scarva Earthstone Original White matures between 1180°C-1280°C" The lithium will have a big effect on the COE of the glaze. I did have some Lithium Carb but I could never get it to go through a sieve it was so coarse – so guess what – I gave up on it! Looks like I paid the price Incidentally, where I have used this glaze but with addition of very small amounts of oxides (nickel and cobalt), I seem to have escaped without the crazing. Link to comment Share on other sites More sharing options...
Mark C. Posted November 18, 2016 Report Share Posted November 18, 2016 It does probably have quite high expansion with all the soda feldspar. Lithium will help the crazing. If you have no lithium carbonate you could swap out say 5 of the soda feldspar for a lithium feldspar (if you have that) and see if it fixes the crazing. Is it leaking out through the bottom? Could be that the clay is underfired even at cone8. Usual rubbish from the company that "Scarva Earthstone Original White matures between 1180°C-1280°C" The lithium will have a big effect on the COE of the glaze. I did have some Lithium Carb but I could never get it to go through a sieve it was so coarse – so guess what – I gave up on it! Looks like I paid the price Incidentally, where I have used this glaze but with addition of very small amounts of oxides (nickel and cobalt), I seem to have escaped without the crazing. Put you lithium material in blender wet and grind for 5 minutes-it will sieve easy after that.Blenders are cheap at thrift stores Link to comment Share on other sites More sharing options...
Celia UK Posted November 18, 2016 Report Share Posted November 18, 2016 Incidentally, where I have used this glaze but with addition of very small amounts of oxides (nickel and cobalt), I seem to have escaped without the crazing. Oxides definitely make a difference to the glaze formula - others will know if it's the expansion - that will be why they didn't craze. This glazing business is very frustrating....I sympathise Oly. Link to comment Share on other sites More sharing options...
glazenerd Posted November 18, 2016 Report Share Posted November 18, 2016 Soda feldspar 70 52 Bentonite 3 EPK 5 Lithium Carb 3 Spodumene 15 Dolomite 7 8 Zinc oxide 5 4 Flint (or quartz) 12 15 COE 7.59 COE 6.78 Stoneware clay typical COE 5.75 Main problem – the jug leaks! ................actually fired to more like cone 8. You fired a C6 clay body to C8: and still have weeping problems. This tells me either you need to change your firing schedule to mature the clay, or this perticular clay body is under-fluxed. Nerd EDIT NOTE: a vitrified clay body will not weep, regardless of glaze application. http://community.ceramicartsdaily.org/topic/15077-nerds-vitrification-test/?hl=%2Bnerds+%2Bvitrification+%2Btest Link to comment Share on other sites More sharing options...
Min Posted November 19, 2016 Report Share Posted November 19, 2016 Nerd, I believe this is a ^4-^9 clay. Oly, can you get a clay with a narrower firing range or have you taken this to clay to ^9 then checked for porosity/absorption? If it's vitrified at ^9 you could try a high fire glaze instead of the ^6 one. Link to comment Share on other sites More sharing options...
glazenerd Posted November 19, 2016 Report Share Posted November 19, 2016 There are 25,000 plus members on this forum: I do believe it is petition time. We need to send a petition to the various clay companies demanding that they stop the practice of "ranging" cone. Specify a single cone, or at most 5/6 or 9/10... etc. Nerd Link to comment Share on other sites More sharing options...
ayjay Posted November 19, 2016 Report Share Posted November 19, 2016 In defence of ES5: I use it regularly. I bisque to 1050°C and ^6 glaze fire to 1210°C with a 15 minute hold. I did an absorption test on some pieces a couple of years back and got a figure of either 1.2. or 1.6. I can't quite remember which it was, but I know I was satisfied with it at the time. Link to comment Share on other sites More sharing options...
bciskepottery Posted November 19, 2016 Report Share Posted November 19, 2016 There are 25,000 plus members on this forum: I do believe it is petition time. We need to send a petition to the various clay companies demanding that they stop the practice of "ranging" cone. Specify a single cone, or at most 5/6 or 9/10... etc. That number is registered members . . . not all active, etc. I doubt you would get more than a couple hundred signatures to a petition (and that is generous). It is not only the manufacturers, but the schools and community studios who order and make students use multi-range clays. And one would figure those places would know better. Link to comment Share on other sites More sharing options...
glazenerd Posted November 19, 2016 Report Share Posted November 19, 2016 Bruce: Point taken! Sad commentary that schools promote the mindset that this practice is acceptable. Perhaps I will just start putting up the email address's of the clay companies, so people can register their complaints and problems: perhaps that will change this trade practice. Nerd Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted November 19, 2016 Report Share Posted November 19, 2016 If they would just specify things better it would go a long way, schools can keep using clay over a wide firing range. Why not put data up for incremental cone firings instead of saying matures over 6-8 different cones. Link to comment Share on other sites More sharing options...
Babs Posted November 19, 2016 Report Share Posted November 19, 2016 You'll have to pay for what you get! With knowledge you can use, dare I say, any clay successfully....... In this case I'd say, glaze is inappropriate. Pushing the biscuit a bit. Stop buying that clay if it gives you results not wanted. Link to comment Share on other sites More sharing options...
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