Chantay Posted May 5, 2014 Report Share Posted May 5, 2014 If learning from your mistakes makes you smarter then I should be a genius by next week. So my last kiln load was a disaster. Over half the stuff went in the trash. Kiln over fired again. Not sure why this time. A new problem was some of the glazes were very thin. I had even taken some water off the tops of the buckets. I was thinking this may be normal for glazes that have sat awhile? Change in air temp? Studio fairies jacking with me? Another idea is 1. I switched to new clay, it needs thicker glaze? 2. I'm throwing thinner with said clay, so it's soaking up less glaze? Any and all wisdom, even snappy comments, are welcomed. Link to comment Share on other sites More sharing options...
Mark C. Posted May 5, 2014 Report Share Posted May 5, 2014 Clay thickness can affect how thick or thin a glaze will adhere to pots Meaning a real thin bowl will suck up less thiockness than say a thiock walled pot of same clay so to get the same affect a thin bowl need to be dipped longer than a thick walled pot to apear the same switching bodies takes time learning the differences In ceramics the studio gremlin is always lurking Also some bodies may take more or less glaze thickness to get same glaze affects as other bodies I work with Porcelain and that in my norm but say when I use a body that is called 1/2 and 1/2 for slab work it takes more thickness of glaze to look the same as my usual porcelain as it has 1/2 of another clay body in it other than porcealin All this takes time to get dialed and is one of the many reasons folks suggle with glaze applications Its actually one of the things I like about ceramics as it takes a long time to master but I'm a fire /glaze potter Mark Link to comment Share on other sites More sharing options...
Babs Posted May 5, 2014 Report Share Posted May 5, 2014 Chantay I think it's a no no to throw out water from the top of your settled glaze, you are throwing out soluble stuff needed in you glaze, and if the glaze worked ok last time then you're also concentrating the ingredients by throwing away the water, and inadvertently perhaps getting. a, a thicker glaze application and b, a slightly, or not, different glaze. To floc or defloc that is the question????? Thinner ware will certainly alter the amount of glaze taken up. Porosity of new clay body may also be a factor. Did you bisque to the same cone? Bisque kiln packed as usual? Don't you just loooove pottery?? Consolation: not alone! Link to comment Share on other sites More sharing options...
Chantay Posted May 5, 2014 Author Report Share Posted May 5, 2014 Old clay body and new clay body are both cone 6 stoneware. The new red clay I'm using is Redrock by Standard. The website states it is cone 3-6. I normally bisque to cone 04. I'm thinking of firing to 03 for the next bisque to see if the body being a little more open helps it take on the glaze better. Not sure how I am going to glaze fire. Last firing the top shelf hit cone 7 and the bottom was cone 5. The clay warps at 7 and glazes blistered, probably from cooling to fast. The glaze firing previous I had gotten the kiln to even out by stratigic loading. New question. Is there any trick to firing large platters? I have very short kiln post so I can put a shelf very close to the surface. I've found out if I put a shelf to high above them, they over fire. They are so big that I can't fit the bottoms on a half shelf. Do you put two shelves at the same level and put the dish in the middle? Babs, I had seen people take water off the top of a glaze at a studio where I was attending. Didn't seem to have any effect. It didn't seem to effect the glaze I did it too. Was one of the ones that came out OK. Just to say, that glaze had sat almost two weeks and the water at the top was clear. Link to comment Share on other sites More sharing options...
Denice Posted May 5, 2014 Report Share Posted May 5, 2014 The longer I work with clay the more I test and I have been working with clay for over 40 years. If you haven't got a test kiln get one they are your best investment, they save you the time and materials of that bad firing that you threw away. They didn't have test kilns with built in pyrometers when I bought mine, I wish mine had one. I am getting ready to glaze a 5'x6' bas relief mural, I have made test tiles for it that mimic the many different areas of textures and design. I even retest a glaze that I have just made a new batch of even though I have made this glaze before. Occasionally glazes will turn out a little different than the test firing but it's usually something I can live with. Denice Link to comment Share on other sites More sharing options...
neilestrick Posted May 5, 2014 Report Share Posted May 5, 2014 Old clay body and new clay body are both cone 6 stoneware. The new red clay I'm using is Redrock by Standard. The website states it is cone 3-6. I normally bisque to cone 04. I'm thinking of firing to 03 for the next bisque to see if the body being a little more open helps it take on the glaze better. Not sure how I am going to glaze fire. Last firing the top shelf hit cone 7 and the bottom was cone 5. The clay warps at 7 and glazes blistered, probably from cooling to fast. The glaze firing previous I had gotten the kiln to even out by stratigic loading. New question. Is there any trick to firing large platters? I have very short kiln post so I can put a shelf very close to the surface. I've found out if I put a shelf to high above them, they over fire. They are so big that I can't fit the bottoms on a half shelf. Do you put two shelves at the same level and put the dish in the middle? Babs, I had seen people take water off the top of a glaze at a studio where I was attending. Didn't seem to have any effect. It didn't seem to effect the glaze I did it too. Was one of the ones that came out OK. Just to say, that glaze had sat almost two weeks and the water at the top was clear. Firing to 03 instead of 04 will make your body tighter, not more open. 03 is hotter than 04. Yes, you can put two half shelves on a row and have the pot in the middle. Just make sure your shelves sit even. When you glaze a pot, the pot must soak in the water in the glaze, leaving the glaze material deposited on the surface. X amount of water must be take in for X amount of glaze material to be on the pot. If the pot is very thin, it cannot take in X amount of water, and your glaze will be too thin. In these cases you need to let the pot dry a bit and glaze again. Do not let the glaze dry completely or the first coat will slump off when you re-dip. The other option is to glaze the inside first, let it dry completely and then glaze the outside. Throwing thin is good, but throwing too thin causes problems. Link to comment Share on other sites More sharing options...
PSC Posted May 5, 2014 Report Share Posted May 5, 2014 Taking water off the top is fine as long as it is completely clear. Not staggering half kiln shelves is fine afterall they make whole kiln shelves, but if you start making a lot of large platters you might want to invest in a whole shelf to fire them on. I use a thin sprinkling of grog on a whole shelf to fire platters on so as to help it not crack in the firing. Don't bisque at 03 for a more open body 03 is hotter than 04 so will make for a less open body and will absorb less glaze. You need to learn your kiln. My kiln i know needs at least a 8" post for the bottom shelf post to not underfire. The top does better with staggered half shelves so most my loads the 7" stuff is at the bottom, the wide stuff in the middle so i can use whole shelves and towards the top i stagger the half shelves or have tall stuff. Link to comment Share on other sites More sharing options...
Chantay Posted May 5, 2014 Author Report Share Posted May 5, 2014 Firing to 03 instead of 04 will make your body tighter, not more open. 03 is hotter than 04 OK, it was early, need coffee. I'm just wondering how many pots I have to throw in the trash before I 'learn" this kiln. No new equipment for a while. Just had to put out for a new wheel. I thought I had it figured out with the last load. I have a glaze that can fire to cone 7, but my clay doesn't like it. I'm wondering how much an exhaust fan would help. I saw plans for a home made one that I'm sure I can whip out. At least with all the duds, I'm getting lots of practice. I think part of the frustrating part is I had plans to become more production oriented. IE: a whole load of mugs, a whole load of bowls, a whole load of plates. But with the temp variations in the kiln that isn't going to happen. I'm thinking, platters on bottom, bowls in the middle, mugs on top. Link to comment Share on other sites More sharing options...
williamt Posted May 5, 2014 Report Share Posted May 5, 2014 Was the old clay red also? More iron in the new clay, acting as addition flux? I have been able to get good coating on thin ware brushing rather than dipping. One of the low flow kiln vents might help even out the temp. Have you used cone packs on each shelf to determine variation? Kiln gremlins must be out. I had my kiln error out for not ramping fast enough the other day. Luckily it was at the end of the firing and the cone bent to nearly 5. 5 being where I was going. Most pieces ok but a couple under fired. Pottery is fun!!! Link to comment Share on other sites More sharing options...
Min Posted May 5, 2014 Report Share Posted May 5, 2014 Sorry to hear you had such a frustrating load of pots. Sounds like you have a number of problems going on at the same time. Thin glazes, do you measure the SG on glazes that work so you can replicate them in the future? Doesn’t take long to do and is helpful until you get to know by sight and how they move in the bucket how thick they should be. If your glaze doesn’t contain water soluble materials it’s okay to scoop off some water, if it does then better to let it evaporate You also mentioned your clay warps at ^7 and you had blisters that you thought were from cooling too fast. Glaze blisters are quite often from the clay gassing out during a glaze fire what wasn’t burned out during the bisque. Did you stack the pieces that show blisters when you bisqued them and how fast do you bisque fire dark clay? Slowing the firing down for the last couple hundred degrees and doing a soak during the glaze fire might allow blisters to heal over. On the shelf that went to ^7 do you have any bloats? Last thing, if your kiln is firing cooler on the bottom I wouldn’t put a shallow platter on short posts there. The kiln shelves add lots of mass that is going to slow the temp rise in that part of the kiln. Put the most mass in the hot part of the kiln to help balance it out. Less mass at the bottom where it is cooler. Link to comment Share on other sites More sharing options...
bciskepottery Posted May 6, 2014 Report Share Posted May 6, 2014 Are you using Highwater's Red Rock (not Standard)? That is a pretty tight clay body -- shrinkage is only 10% and absorption less than 1% at cone 6. I bisque to Cone 05 and glaze Cone 6. I've had some bloating at Cone 6 -- but my kiln fires hot and I suspect that was the issue. Firing in the cooler part of your kiln might be necessary to avoid bloating/warping. I fire large platters on full shelves and I generally leave at least 1" clearance to the next shelf. Your shelves retain heat and cool more slowly than your pottery. So, if you have flat items -- like platters -- you don't want the next layer of shelves too close so that the heat from that shelf layer affects the flat items on the shelf below. On large platters, I'll also use clay cookies and/or flat clay slats beneath the platter to allow air circulation during cooling -- again, because the shelves retain heat after the wares have started to cool. Link to comment Share on other sites More sharing options...
timbo_heff Posted May 8, 2014 Report Share Posted May 8, 2014 Babs, I had seen people take water off the top of a glaze at a studio where I was attending. Didn't seem to have any effect. It didn't seem to effect the glaze I did it too. Was one of the ones that came out OK. Just to say, that glaze had sat almost two weeks and the water at the top was clear. Babs is right: Don't pour water off: solubles within! Floc /Defloc to fix glaze thickness Link to comment Share on other sites More sharing options...
Chantay Posted May 9, 2014 Author Report Share Posted May 9, 2014 Thanks for the advice everyone. Bruce, yes it is Highwaters red rock. I haven't had any problems with this clay except for when I over fire it. When I put a platter on stilts it warped. Maybe your large cookies is a good idea. I will try it out. I'm sure I can get the kiln to not over fired if loaded bette Link to comment Share on other sites More sharing options...
neilestrick Posted May 9, 2014 Report Share Posted May 9, 2014 Thanks for the advice everyone. Bruce, yes it is Highwaters red rock. I haven't had any problems with this clay except for when I over fire it. When I put a platter on stilts it warped. Platters on stilts will warp with pretty much any clay that fires to vitrification. Easier to dry foot and sit it on the shelf. Link to comment Share on other sites More sharing options...
Babs Posted May 9, 2014 Report Share Posted May 9, 2014 Still firing with kiln sitter witness cones, log of firing ra de ra, I cannot understand the computer prob. of overfiring! Some one explain this in dinosauric terms. I have never found a kilnl which will fire evenly thro'out and so have to use a no. of glazes, those with mature a cone or 2 up or down depending on the area of the kiln they are placed...... What am I missing in reading this post/ The glaze uptake is one thing, the glaze settling another, but the overfiring Leaves me in fear ofthe day I have to dump old sparkie and get that front loader I have been promising myself. Ican get the evenig of the temp with strategic soaks and density of packing but is the calibration of the top temp acheived out of control?? Link to comment Share on other sites More sharing options...
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