Uliana Posted May 30, 2020 Report Share Posted May 30, 2020 Cheers! I thank you very much if anyone can consult. I don't know why in the black or red ceramic paste (which I have high temperature), my faldespatico base enamels do not cover this clay. The enamels come out with bubbles.., although in white clay they work well for me. I understand that black clays contain ox iron and manganese.. Link to comment Share on other sites More sharing options...
neilestrick Posted May 31, 2020 Report Share Posted May 31, 2020 Can you tell us more about the clay bodies, what temps you're firing to each time, process, etc? Link to comment Share on other sites More sharing options...
Uliana Posted May 31, 2020 Author Report Share Posted May 31, 2020 Thanks for answering. I don't understand why enamels react so differently in the different types of body. And how can I configure the enamel with different paste. I kiln in an oxidizing atmosphere / cones 8-9 1. 100*c/h - 500*C - 0:00 2. 5h - 1070*C - 0:00 3. 3h - 1257*C - 0:20 4. End Clay I use for high temperature: 1. White chamotte refractory paste (gray refractory paste 0-0.2 mm) SiO2 ox of silisio 63,92 Al2O3 ox of alumina 26,48 Fe2O3 ox iron 1,06 TiO2 ox titanium 1,52 CaO calcium ox 0,14 MgO magnesium ox 0,18 Na2O sodium ox 0,24 K2O potassium ox 1,60 MnO manganese ox <0,01 L.O.I ….. 4,26 Plasticity (Atterberg) L.L …..…34 I.P ……..16 2. Black chamotte refractory paste (black refractory paste 0-0.2 mm) SiO2 ox of silisio 41,62 Al2O3 ox of alumina 30,17 Fe2O3 ox iron 13,86 TiO2 ox titanium 1,49 CaO calcium ox 0,28 MgO magnesium ox 0,62 Na2O sodium ox 0,22 K2O potassium ox 1,37 MnO manganese ox 0,36 MnO2 manganese ox 2,79 L.O.I………7,37 Plasticity (Atterberg) I.P.........22 Link to comment Share on other sites More sharing options...
neilestrick Posted May 31, 2020 Report Share Posted May 31, 2020 @Uliana When you say enamels, do you mean glazes? Link to comment Share on other sites More sharing options...
Uliana Posted May 31, 2020 Author Report Share Posted May 31, 2020 sorry.. Yes, I'm talking about glazes, the good translator sometimes translate incorrect. 18/5000 Link to comment Share on other sites More sharing options...
Min Posted May 31, 2020 Report Share Posted May 31, 2020 The two dark clay test tiles with the large bumps, are the bumps intentional or did they occur in the firing? With dark clays containing lots of iron and manganese like the one you are using it's really important to bisque fire them in a well vented firing. How are you doing your bisque firing? Also, what is the temperature or cone number your dark clay is rated to fire up to? Link to comment Share on other sites More sharing options...
Uliana Posted May 31, 2020 Author Report Share Posted May 31, 2020 11/5000 Thanks Min! The bumps they occurred in the fairing. Is not intentional! Range of this black clay is: 1200ºC-1240ºC My bisque is 1010ºC The faring wis glaze is at 1257ºC I am a beginner in the firing, I thanks for any info on that topic. Most of my glazes in that clay rich in iron and manganese get pitted or bubble.., although in white clay I don't have this problem! I don't know why? how can these defects be avoided? It may be that I need to add something in glaze ? I am thinking about Bentonite ? Link to comment Share on other sites More sharing options...
Min Posted May 31, 2020 Report Share Posted May 31, 2020 8 hours ago, Uliana said: Range of this black clay is: 1200ºC-1240ºC My bisque is 1010ºC The faring wis glaze is at 1257ºC By firing to 1257C you could very well be overfiring the clay, this can be one cause for the bumps (called bloats) in the claybody itself. The bisque firing schedule is really important with dark iron/manganese claybodies. The kiln needs to be well vented and not too crowded with pots. There needs to be time for the organic materials to cleanly burn off in the bisque. If you have a controller on your kiln then you need to slow the firing down to 100 C an hour from 150C up to 325C and a very slow 50C an hour between 700C and 900C. These are the temperature zones that the carbons need time to burn out. If they don't then what happens is the gasses that didn't burn out in the bisque try to escape during the glaze firing but they can't so the clay can get bloats and the glaze has problems like you are having. Do you have a controller and a vent on your kiln? I hope this is clear for you when you translate it. Link to comment Share on other sites More sharing options...
Uliana Posted June 1, 2020 Author Report Share Posted June 1, 2020 Min, thank you very much for the reply! Yes, I have the temperature controller. I'm going to change the settings of the program. That topic is very interesting to me, do you know any book to know more about it? Through love for clay I will improve English =) I hope I will be successful, and here I will leave the photos of my experiments. Link to comment Share on other sites More sharing options...
Min Posted June 2, 2020 Report Share Posted June 2, 2020 Your English is just fine, I was trying to avoid words that might be difficult to translate. You can read about body bloating here, this is an excellent website with a huge amount of information on many ceramic subjects. Page 166 from "The Ceramic Process" which is available here as a preview also mentions body bloating. Lastly, there is a really good thread on firing high manganese clay here. For the bubbles and blisters search those terms in this forum and also on the first one I linked to above. Link to comment Share on other sites More sharing options...
Uliana Posted June 2, 2020 Author Report Share Posted June 2, 2020 Thank you very much for links and attention! Link to comment Share on other sites More sharing options...
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