PottaFella Posted June 14, 2016 Report Share Posted June 14, 2016 Firing stoneware pot at cone 6/7 it weeps giving a sllghtly damp bottom to pot. what can I do? refire to higher temp? Clay is Valentine ES5 Alumina matt glaze (M Bailey recipe) is: Soda Feldspar 70 China clay 13 Dolomite 5 Whiting 5 Quartz 3 Link to comment Share on other sites More sharing options...
Mark C. Posted June 14, 2016 Report Share Posted June 14, 2016 I would start listing to my guitar gently weeps by Eric Clapton-turn it up loud while looking for another clay body. really was this a cone 10 body fired to lesser temps? of a cone 6 body not working well? Link to comment Share on other sites More sharing options...
Joseph Fireborn Posted June 14, 2016 Report Share Posted June 14, 2016 http://www.valentineclays.co.uk/product/es-5-original ES5 Matures at 2336F or 1280C - This is basically cone 10 claybody. So your pots probably are no where near vitrified and are weeping because of that fact. Link to comment Share on other sites More sharing options...
PottaFella Posted June 14, 2016 Author Report Share Posted June 14, 2016 okay I'd thought cause it says 1180 - 1280 it'd be okay at the cone 6 lower temp Link to comment Share on other sites More sharing options...
Joseph Fireborn Posted June 14, 2016 Report Share Posted June 14, 2016 I know it's stupidly annoying. I don't know why suppliers do this. They should just mark the cone temp that it matures at. It really irks me too. Get a better clay body that vitrifies at your cone 6, and your pots will stop crying tears of sadness. Link to comment Share on other sites More sharing options...
PottaFella Posted June 14, 2016 Author Report Share Posted June 14, 2016 When a manufacturer say 1280 as a top temp, do they actually mean heatwork ie. cone 9? I wonder if that (cone 6) glaze recipe would take going up higher towards 1280, in which case I could re-fire it? or a longer soak? Link to comment Share on other sites More sharing options...
Joseph Fireborn Posted June 14, 2016 Report Share Posted June 14, 2016 Heatwork and temp are different things. But ideally they should give a cone rating, which is heat work required to vitrify that body. It is probably the same thing as the temp they are listing, but yea, that is cone 9-10 clay body for vitrification I am assuming(call them and ask). I really have no idea, their website doesn't give any good details on what the body does at each temp. They don't give absorption rates, which is the most important thing to know for a functional clay body. I mean it could have like a really high absorption rate even at cone 10, we have no idea. They don't tell you. It could be like 5-10% absorption, who knows. I would find a better supplier or find someone who can give you that information at that company. As far as refiring. I have no idea, if the glazes are made for cone 6, they could run off the shelves so be careful. Link to comment Share on other sites More sharing options...
neilestrick Posted June 14, 2016 Report Share Posted June 14, 2016 Re-firing will only help if you can get it to cone 9/10, which your glaze may not handle. You can get away with a less-than-vitrified clay body if your glaze isn't crazed, but that's not ideal, because some day it will craze. Link to comment Share on other sites More sharing options...
PottaFella Posted June 14, 2016 Author Report Share Posted June 14, 2016 I've put out a call to the clay formulators to find out about absorbtion etc. These Valentines/Scava clays are very well thought of here in UK, I think everyone uses them Think I'll try refiring one pot to cone 8-9 (1263-1280) I'll have to go my the electric controller but put some cones in so I can see after where the heatwork got to. I'l prob set the top temp to 1265 and give it half hour soak I reckon that will get close to Cone 9. I'll stick the pot on something in case it melts. Link to comment Share on other sites More sharing options...
Joseph Fireborn Posted June 14, 2016 Report Share Posted June 14, 2016 Let us know how it goes. Link to comment Share on other sites More sharing options...
PottaFella Posted June 14, 2016 Author Report Share Posted June 14, 2016 Just found following review on the Scarva site (Scarva formulates this clay and Valentines makes it in England I believe) which raises more concerns over the maturation temperature... "Lovely clay to throw, handles nicely on the wheel and is pretty smooth; my only criticism is that the claimed Tmax of 1280 is perhaps a tad optimistic - dinner plates slump badly at 1260 and the probable Tmax for flat or complex forms is closer to cone 6 at a guess." Link to comment Share on other sites More sharing options...
Joseph Fireborn Posted June 14, 2016 Report Share Posted June 14, 2016 You just need to go straight to the distributor and find out what they know. Random reviews are not always the most accurate. For example if you google Frost Porcelain Cracks, almost every review is about how the clay body is impossible to work with, but several people on here use it exclusively and I have used it as well and didn't have any major cracking problems. People usually only voice opinion when things are wrong, not when they go right. Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted June 14, 2016 Report Share Posted June 14, 2016 They are useless at giving any information. I want to complain. My clay is also sold as an earthenware stoneware with Recommended Firing Range 1100-1290C. What the duck. Works great at cone9~ Link to comment Share on other sites More sharing options...
PottaFella Posted June 14, 2016 Author Report Share Posted June 14, 2016 They are useless at giving any information. I want to complain. My clay is also sold as an earthenware stoneware with Recommended Firing Range 1100-1290C. What the duck. Works great at cone9~ can you say what clay it is? id always thought cause mine is sold as 'earthstone' it would be fine at all temps within the parameters they give Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted June 14, 2016 Report Share Posted June 14, 2016 They seem to go with the moto once it's bisque we are good to go but 1000c might be a little too low even for us. I bought it from a local guy reselling clay's up north but I am 99% it is this one. Sold as schoolware buff and can go down to £2.50 a bag. http://www.valentineclays.co.uk/product/stoneware-v9a http://www.potterycrafts.co.uk/Products/wab/P1341 I think they are all the same clay. Used it when I went to college for the year and never stopped. Just worked for me. Link to comment Share on other sites More sharing options...
Celia UK Posted June 14, 2016 Report Share Posted June 14, 2016 I don't think it's the same clay as schoolware buff Joel. Scar a says ES5 vitrifies at 1200oC. It's a very popular clay amongst Anglian Potters Association - around 400 members from hobby potters to professional. We have 3 clay stores across the region and buy in bulk for our members and this is one of the best sellers. Not sure if the composition tells anyone with the knowledge any more about it:- 64.84% SiO2 1.05% TiO2 23.57% AL2O3 0.75% Fe2O3 0.08% P2O5 0.22% CaO 0.31% MgO 2.57% K2O 0.72% Na2O Total contraction at 1200oC - 13.80% Thermal expansion 500oC - 0.260 600oC - 0.320 But no absorption listed. Link to comment Share on other sites More sharing options...
Joe_L Posted June 14, 2016 Report Share Posted June 14, 2016 I did some tests on ES5: Bisqued at 999 then 2nd firing to 1240'C (climbing at 130'C/hr for last hr) soak 20mins. This puts Cone8 fully down in my Rohde 43L electric kiln, may even be higher but I hadn't put a cone 9 in the pack that time. There was no noticeable dampening of newsprint left underneath a cyclider of water. ES5 shrinkage after firing was 12%; warp was <1.5mm on a 120mm clay bar on horizontal stilts at 100mm spacing; absorption after 24hrs immersion was about 5-6% +-2%. (N.B. The absorption measurement was very crude as my scales only had a 1g resolution. I've now got a higher resolution scale so I will repeat the absorption test and report back). Joe Link to comment Share on other sites More sharing options...
PottaFella Posted June 14, 2016 Author Report Share Posted June 14, 2016 I did some tests on ES5: Bisqued at 999 then 2nd firing to 1240'C (climbing at 130'C/hr for last hr) soak 20mins. This puts Cone8 fully down in my Rohde 43L electric kiln, may even be higher but I hadn't put a cone 9 in the pack that time. There was no noticeable dampening of newsprint left underneath a cyclider of water. ES5 shrinkage after firing was 12%; warp was <1.5mm on a 120mm clay bar on horizontal stilts at 100mm spacing; absorption after 24hrs immersion was about 5-6% +-2%. (N.B. The absorption measurement was very crude as my scales only had a 1g resolution. I've now got a higher resolution scale so I will repeat the absorption test and report back). Joe is the absorbtion a measure of water take-up? Link to comment Share on other sites More sharing options...
PottaFella Posted June 14, 2016 Author Report Share Posted June 14, 2016 They seem to go with the moto once it's bisque we are good to go but 1000c might be a little too low even for us. I bought it from a local guy reselling clay's up north but I am 99% it is this one. Sold as schoolware buff and can go down to £2.50 a bag. http://www.valentineclays.co.uk/product/stoneware-v9a http://www.potterycrafts.co.uk/Products/wab/P1341 I think they are all the same clay. Used it when I went to college for the year and never stopped. Just worked for me. I did try the v9a, partly because it was so cheap, I found my glaze pinholed at cone 6 perhaps I could try it at a higher temp Link to comment Share on other sites More sharing options...
Joe_L Posted June 14, 2016 Report Share Posted June 14, 2016 is the absorbtion a measure of water take-up? Yes. I fire a bar of unglazed clay to bisque and again to glaze temperature. Weigh it, soak 24hrs and then weigh again. I've just reweighed it with my better scales and put it in to soak for tomorrow. Joe Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted June 14, 2016 Report Share Posted June 14, 2016 I don't think it's the same clay as schoolware buff Joel. Sorry I meant my two links were the same as what I bought locally. Not the same as ES Link to comment Share on other sites More sharing options...
glazenerd Posted June 15, 2016 Report Share Posted June 15, 2016 Not sure if the composition tells anyone with the knowledge any more about it:- 64.84% SiO2 1.05% TiO2 23.57% AL2O3 0.75% Fe2O3 0.08% P2O5 0.22% CaO 0.31% MgO 2.57% K2O 0.72% Na2O Celia: I find it very hard to believe this clay matures at 1200C [ 2192F] The silica % is lowered, which is the usual protocol for cone 10 to prevent dunting due to free silica/cristobalite formation. The alumina is on the low side as well for a stoneware body- more in line with earthenware. The primary flux is potassium: which is in line with cone 8-9 range. Some comparisons: Generic C10 stoneware body: 64.97 silica, 28.31 alumina, total fluxes: 3.71 >> I would estimate the maturing temp of the body shown above in the cone 8-9 range at minimum. (total fluxes 3.81%) Iron can only be counted as a flux if it is fired in reduction. Nerd Link to comment Share on other sites More sharing options...
Babs Posted June 15, 2016 Report Share Posted June 15, 2016 If retiring put your pots on biscuits/cookies. Glaze will most likely run. Refiring that is😠Link to comment Share on other sites More sharing options...
PottaFella Posted June 15, 2016 Author Report Share Posted June 15, 2016 Going back over notes it looks I like I started using this clay a couple of years ago and first fired it at1240 with a 30min soak, I've since allowed it to creep down to cone 6ish 1210 with 15min soak. I'm going to try refiring a pot using the old firing schedule see if matters improve. Link to comment Share on other sites More sharing options...
Joe_L Posted June 15, 2016 Report Share Posted June 15, 2016 ES5 absorption after firing to 1240C is 1.8%. (Sorry my previous figure was utter fiction, I must have misread my notes. With my old low resolution scales it came out at ~1.5%, which at least is consistent. I also got ~1.5% with the old scales on a test fired at 1220C, but I don't have this to hand to repeat on the new scales.) Joe Link to comment Share on other sites More sharing options...
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