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Gokul

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  1. Babs, I have been try using the synthetic plasticiser to the clay and can share you the results once the clay is ready.
  2. Babs, The crack is happening in the mold itself but it not a end to end crack and its a surface cracks but bit deeper than the usual surface cracks.
  3. Rae, yes we have try adding 5-20% grog to the body but still the cracks are happening in the same area. :-(
  4. Hi, We have been doing the jigger for the first time and the pieces whatever we are making have a cracks in a same pattern in a same location, and we are using Terracotta clay to make the pieces and here I m attaching the cross sectional pieces of the molds., and in the molds I have few doubts and I would like to get clarified so that I can reduce the cracking doors one by one., Does the thick and thin portions of the molds absorbs water differently so that the pieces are cracking ? As you can see the picture of the pieces the cracks are happening in the place where the side wall is connecting with the curved edges, and the cracks are happening only with our terracotta clay and we have tried quite a lot of receipes to avoid cracks but nothing is helping out and the cracks are happening in the inside of the pieces and the outside wall is just fine. Also we have tried jiggering few pieces with our stoneware clay and we havent have any cracks in the stoneware. Does the uneven wall thickness is the reason to get the cracks ? Wi only the Terracotta is cracking and not the stoneware ? Wi the inner wall is cracking and it didnt extend to the outer wall ? Does it anything to do with the plasticity and the composition of the clay? As far as the design is concerned, we make sure theres no undercuts in the design and even the wall is not striaght and it has an angle of 10% for easy releasing., we used to have few issues with our clay body which I was working with Tom (Glazenerd) to solve the issue, but apart from that I would like to know what are the other possible reasons for the cracking.
  5. Tom, Pls find the attached picture of the clay which we are blending and using., These are the two red clays which we are getting from our supplier No.1 Red one seems like the laterite or red soil after I read the article of Dr. sudharsans article abstract and the No.2 seems like more of an alluvial soil I guess so, and we used to get the No.2 most of the time becasue it used to be very good interms of plasticity and there wont be any cracking as well but the No.2 Mines clay is not easily available I can get the material only at the time of summer because the mines will be closed at the time of Mansoon. So we cant and we dont want to rely on the brown one itself then we got the red one (No.1) which is very fine interms of particle size distribution and it has less plasticity ., so right now what we are doing is we get a stock of No.2 clay as and when its available and we mix 50% of No.1 and 50% of No.2 clay and we do our processing and make it into a clay. But still we have the cracks issue so we started adding 1% Sodium Bentonite with the above mixture mentioned and we make it as clay and pug it using the pugmill (Pic Attached) its a deairing pugmill but it dosent have any vacccum attached it and its a good homogeniser. Pls find the attached pic of the process flow chart of our clay making process. And the WOPT of our clay is 23 %. Dry Shrinkage - 6 % Fired Shrinkage - 8% @(cone 08) LOI - 15% @(cone 08) Porosity - 20% @(cone 08) Pls find the wet sieve analysis result below of the two clays Sieve No No.1 No.2 40 0.1 0.2 60 1 0.7 80 2.2 2.5 100 3.8 4.9 120 3.2 3.9 140 7 9.8 170 8 11.1 200 11.2 30.4 230 12.9 15 270 8.7 2.1 300 15.2 15.7 PAN (300+) 26.7 3.7 Total 100 100
  6. Curt, Thanks for your reply, and the top picture is our regular terracotta which is been throwing on the wheel.
  7. Tom, Thank you so much for your detailed study of the issue and I really appreciate your effort and time., and yes I started adding 1% of sodium bentonite to our Terracotta clay body and it seems like it has solved a issue a bit but I m finding the other issues like the clay splitting when it comes out from the pugmill, I dont know whether its related to our crack issue, pls find the attached pic of the clay., and its really difficult for me to add sodium bentonite more than 2% because it has the swelling property which in one side its good interms of slower drying and difficult interms of processing with the regular clay its not mixing well with the clay and the below two pictures are terracotta clay with 1% Sodium bentonite into it, do you think that the splitting isssue is because of adding the bentonite. ?
  8. Thanks for the reply Diesel, We havent use any slip on the clay and we keep the pieces for firing only after its completely dry and sometimes the cracks are just the surface cracks and sometimes its structural cracks, And yes we are doing our own firing with skutt kiln and the pieces are fired at cone 08 in medium fire setting which is I guess its 150 D / hr. Basically I m from India and the clay which we are getting locally in powder form, we process and filter it with 100# (sieve) and pug it and we are using it and selling it all over india for the studio potters and for the schools all over india., and yes the clay seems like lacking of plasticity and we are adding 2% of bentonite to it to make sure the clay has fine plastic particles and as well as the plasticity.
  9. Hi, I have this problem of cracking or clay splitting when throwing in the wheel, pls find the attached picture and also, after firing at cone 08, the clay has a lot of surface cracks and sometimes structural cracks pls find the attached pic, pls advise why this is happening and how to avoid this in future. Thanks.
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