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dolly

Crazing

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Hi there I'm wonder if anyone can help me , I've researched crazing problems in firing think I've tried most of what I have gleaned of Internet and library book, now at the end of my tether.

My problem being I am painting the piece in greenware with velvet underglaze  firing my cwe white earthenware to 1060 which was a recommended temp.by supplier. taking the firing up slowly around 10 11 hours. waiting for kiln to cool down . checking painting ok on piece and touching up anything that isn't . glazing the whole piece stilting . firing at 1060 which takes around 8 hours . come out the kiln perfect . few days later ping.not all pieces . only half. . I was recommended to thin my glaze which I have. still crazing. rub glaze over the crazing and refire  some are successful some aren't . any suggestions please  ann

 

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Try searching in the forum topic areas for "crazing" and you will find a lot of discussions as this is a common problem.

 

What you have is a mis match of body and glaze ... Thinning your glaze is not the answer because the problem is in the actual ingredients in the glaze and clay.

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Are you using a commercial clear or one that you mix yourself?  If it is one you mix yourself, could you post the recipe?  Is this a new container/batch of glaze or one you've been using with success for a while?

 

Crazing (and pinging) occur when, as Chris noted, the clay body and glaze do not fit properly -- the glaze is shrinking more than the clay body, resulting in crazing.  And, the effects of crazing can occur days/weeks/months after the item is removed from the kiln. 

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Crazing is the bane of my life, even though I work in stoneware. The thing with earthenware is that the glaze will eventually craze, even though it doesn't do it in the kiln. With use, the absorbent body takes in moisture from the air and dishwater, which makes it expand slightly, which stretches the glaze so that it splits. 

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thank you for your replies. the glaze is a earthenware glaze powder which I mixed up myself. this glaze was fine and had no grazing. but i changed my clay distributor, that I think that's where my problem started . I wondering If I should fire my Clay to 1100 or higher then fire the glaze 1060 because I know it's not the glaze at fault here. I have 20 x packs of this clay . feeling worried .

I'm not familiar with making my own Glazes , and it's not a thing I really want to get into. too much science. just want a a glaze to fit this clay. I throw pots on the wheel then alter them sculpting all manner of subject. which are usually vases so need to be watertight , So the clay is not all uniform thickness. do you think that could be the problem. all my pieces are dry when I fire .went to a big pottery show at the weekend and was shock to see pots at £450.00 with crazing on them tut tut . Will take a look at previous post on crazing as advised thank you

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Earthfan  you just said what  I've been thinking just like the vibrant colour i get with the earthenware. I looked at a super Kiln yesterday at the show , when i mentioned i worked in earthenware. He looked at me in disdain. I think he must have been a clay snob .

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hi there Don't understand do I add silica to the glaze , I think I will have to study Glazes , didn't want to go down that path as science and me do not get on lol. thank you for your help all. just got to go back to the basics.Pottery is a love hate relationship with me at the moment. want to walk away from it , but have got so near to what i want to achieve .never had a problem with crazing when first starting out , achieved and overcome  so many other things . I know i should change clays and go with stoneware ,but i want the vibrant colours eathernware  gives me , just need my creation to hold water.but my heart sunk when i went to arts in clay and saw even the professional had crazing going on . so i think what chance do i have . when i finish a piece i always put water in it to see if it's watertight , and will hold and be a usable object. the science behind all this glaze preparation is of no interest to me , all i want is a glaze that seals my work. I've got to many other thing with clay that excites me throwing altering designing firing painting and seeing my pieces come to life. it's a passion that I can't walk away from and at time wish i could. does my head in . thank you all for your input nice to speak to people that have the same love for ceramics. my Husbands Eyes glaze over when I even attempt to talk about pottery. 

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Every glaze does not fit every clay. Not even close. You've either got to do a lot of testing of clay and glazes to find matches that work, or you can alter the glaze. Increasing the silica in the clay will reduce crazing. Take 200 grams of powdered glaze and add 3% silica (6 grams) to it. Blend, dip a tile, add another 3%, blend, dip a tile, and repeat until you've reached 15% silica. It's not super exact in the higher amounts, but it will get you close. Once fired you can see which tile is best and do another round of more precise tests to get it perfect.

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thank you will give that a go will have to get some silica though, hav

e spoken to the supplier , he advised me to fire my bisque higher 1100 and fire my glaze 1060 so going to try that also ordered some stoneware going to give that a go. as he said matching glazes for stoneware is a lot more forgiving here's hoping, thank you 

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thank you will give that a go will have to get some silica though, have spoken to the supplier , he advised me to fire my bisque higher 1100 and fire my glaze 1060 so going to try that also ordered some stoneware going to give that a go. as he said matching glazes for stoneware is a lot more forgiving here's hoping, thank you 

Good luck with the stoneware route.  I have far, far more glaze problems at ^6 than ^06.  And there is less choice of ready-mixed commercial glaze.  

 

I'm also in Essex, where do you buy your stuff from?

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Every glaze does not fit every clay. Not even close. You've either got to do a lot of testing of clay and glazes to find matches that work, or you can alter the glaze. Increasing the silica in the clay will reduce crazing. Take 200 grams of powdered glaze and add 3% silica (6 grams) to it. Blend, dip a tile, add another 3%, blend, dip a tile, and repeat until you've reached 15% silica. It's not super exact in the higher amounts, but it will get you close. Once fired you can see which tile is best and do another round of more precise tests to get it perfect.

Dolly, I think your supplier is selling you a pup when he advises you to go away from your earthenware into stoneware, which can lead you to many more things to adjust.

Please try Neil's suggestion before you invest time/money in stoneware. If it helps, think of it as cooking (recipes) rather than science (formulas).

Good luck!

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Just put my pieces in the kiln programmed it to 1100 . going to take it slow . babysitting the kiln ,  then glazing at 10.60. then waiting to see if there's any crazing. in the next few weeks.fingers crossed . if that fails going down the silica route. did order some stoneware . only 2 packs. so not broken the bank. will play with that at a later date, going to concur the earthenware first.  and chilly I'm from Southend  , I ordered this particular clay from Castree . but my glaze is from clay cellar. but do like to visit Brickhouse. unfortunately they don't deliver. thanks for all your advice very much appreciated .

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"went to a big pottery show at the weekend and was shock to see pots at £450.00 with crazing on them tut tut"    If people pay 450 pounds for a pot, they are not going to use it, so it won't matter if it is crazed.   Many years ago, I went to an exhibition of work by Greg Daly, who writes books on glazing. The work was  beautiful big platters with up to 4 different stoneware glazes layered in various ways. I was horrified to see that the glazes were about a centimetre thick and thoroughly crazed. I attended his seminar and, of course, he wasn't giving away his glaze recipes. Which was OK by me because I didn't want them.

 

My latest idea is to raw glaze to stoneware temperature, and decorate at a lower temperature. Still only two firings. Haven't done it yet.

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