cbarnes Posted November 15, 2016 Report Share Posted November 15, 2016 larger pieces are cracking around the base on cone 6 refire. I'm using a porcelain clay, throwing on the wheel, drying on a wood bat after pulling off with wire and covering with thin plastic (I use drycleaner bags). in a garage so ambient temperature varies. when throwing I'm using a lot of water but clear it up with sponge and compress the bottom. definitely dry before firing to cone 04 bisque. Seems to crack mainly around where I trimmed but not always any ideas why this is happening? should I turn the piece once its leather upside down for more even drying? maybe trimming to thin? at a loss. about a third of my larger items are having this occur. platters & bowls - 12 - 17" bases. Link to comment Share on other sites More sharing options...
Marcia Selsor Posted November 15, 2016 Report Share Posted November 15, 2016 Hi C, Beautiful brushwork. Sorry it cracked. I think it is a combination of 2 things. One is the thickness got too thin around the foot and secondly,the overhang of the lip is quite large. Here is a tip for watching your thickness near the foot. Leave more clay. Put 2 thumb tacks close to where you think you'll be making the foot.one on either side of where the foot will be. Flat top on the inside of the plate. As you trim your tool will hit the point and you'll know the thickness.For an overhang like you are doing, don't go much thinner than the thumb tack tip. Marcia Link to comment Share on other sites More sharing options...
Min Posted November 15, 2016 Report Share Posted November 15, 2016 'larger pieces are cracking around the base on cone 6 refire." Think it's likely your firing schedule for refires on large flat pots that is the problem if they made it through the first glaze fire okay. Have to slow the kiln down to a crawl through both inversion temperature ranges. From 400F thru 500F should get you safely through the lower one (both on heating up and cooling down) and then from 1000F thru 1100F. Gorgeous brushwork! Link to comment Share on other sites More sharing options...
cbarnes Posted November 15, 2016 Author Report Share Posted November 15, 2016 Hi C, Beautiful brushwork. Sorry it cracked. I think it is a combination of 2 things. One is the thickness got too thin around the foot and secondly,the overhang of the lip is quite large. Here is a tip for watching your thickness near the foot. Leave more clay. Put 2 thumb tacks close to where you think you'll be making the foot.one on either side of where the foot will be. Flat top on the inside of the plate. As you trim your tool will hit the point and you'll know the thickness.For an overhang like you are doing, don't go much thinner than the thumb tack tip. Marcia great! thank you I appreciate the tip. i'll try it this weekend! I love making these large pieces, and painting the detail, but boy is that a lot of time put in for a failure. such is the life of a potter. Link to comment Share on other sites More sharing options...
cbarnes Posted November 15, 2016 Author Report Share Posted November 15, 2016 'larger pieces are cracking around the base on cone 6 refire." Think it's likely your firing schedule for refires on large flat pots that is the problem if they made it through the first glaze fire okay. Have to slow the kiln down to a crawl through both inversion temperature ranges. From 400F thru 500F should get you safely through the lower one (both on heating up and cooling down) and then from 1000F thru 1100F. Gorgeous brushwork! thank you! I've been using the kiln controller fast glaze setting. I guess its time to learn to set the ramp up/down times myself. Link to comment Share on other sites More sharing options...
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