glazenerd Posted March 21, 2016 Report Share Posted March 21, 2016 In reading an article in the Ceramic Industry trade magazine I came across the following commentaries: Firing in a gas kiln appears to produce better results than firing in an electric kiln. The bodies fired in the gas kiln were more compact than the bodies fired at the same temperature in the electric kiln, perhaps due to the circulation and composition of the combustion gases. Additionally, the variation in reactivity of the bodies under the interactions that led to the formation of liquid phases (illustrated by the determined values of the compactness of the fired bodies) was similar to that indicated by the results of the thermal and X-ray diffraction analyses. The degree of vitrification of the fired bodies was further proof of their reactivity. This article is referencing the effects on clay in a gas kiln: not glazes. Citing the absence of oxygen in the kiln environment actually caused the clay body to experience a higher degree of fluidity (liquid phases) resulting in a higher degree of vitrification. More specifically, mullite and corderite formations: both refractory materials. Can anyone who fires in both electric and gas kilns testify to the differences in density or vitrification? Found the conclusions and commentaries in this article interesting. Nerd Link to comment Share on other sites More sharing options...
bciskepottery Posted March 21, 2016 Report Share Posted March 21, 2016 Apples and oranges if the electric was fired oxidation and the gas reduction; or was the gas fired oxidation? Link to comment Share on other sites More sharing options...
glazenerd Posted March 21, 2016 Author Report Share Posted March 21, 2016 Think most people view it as apples and oranges: apparently some science types disagree. Then again, I have found myself disagreeing with several long held assumptions. due to the circulation and composition of the combustion gases. Apparently you missed this line-- reduction Nerd Link to comment Share on other sites More sharing options...
Pres Posted March 21, 2016 Report Share Posted March 21, 2016 Bruce in the non quoted area, glazenerd states that. . . Citing the absence of oxygen in the kiln environment. If I am correct to assume that absence of oxygen means reduction environment, then it would decidedly be an apples oranges comparison. I envy those of you our there that have the space, the zoning allowances and the where withal to run a gas kiln. As I live in the middle of town, have a small garage studio with no surrounding area to have a kiln shed, I am forced to use electric. At the same time, the understanding of the chemistry at cone 6 whether oxidation or reduction has improved immensely since I started in this range back in the 70's. For that I am truly thankful. best, Pres Link to comment Share on other sites More sharing options...
Guest JBaymore Posted March 21, 2016 Report Share Posted March 21, 2016 Since FeO is a flux on silica, if the kiln is fired in reduction, and the reduction occurs when the body is still gas permeable to the CO molecule, AND there is some level of Fe2O3 present, then the added flux would likely produce a more fluid melt. This impact might be what they are talking about. Heavily iron fluxed glass in a body can promote brittleness... so generally too much is not a good thing even though it can decrease Apparent Pororsity figures.....so I can't believe that they are talking about that kind of level. Never tested the two directly against each other for something like MOR. (same body in electric and reduction gas) best, ................john Link to comment Share on other sites More sharing options...
glazenerd Posted March 21, 2016 Author Report Share Posted March 21, 2016 John: Ty for answering my natural curiosity. I read this article and thought: why would reduction have such an effect? Nerd Link to comment Share on other sites More sharing options...
Magnolia Mud Researdh Posted March 21, 2016 Report Share Posted March 21, 2016 In reading an article in the Ceramic Industry trade magazine I came across the following commentaries: Firing in a gas kiln appears to produce better results than firing in an electric kiln. The bodies fired in the gas kiln were more compact than the bodies fired at the same temperature in the electric kiln, perhaps due to the circulation and composition of the combustion gases. Additionally, the variation in reactivity of the bodies under the interactions that led to the formation of liquid phases (illustrated by the determined values of the compactness of the fired bodies) was similar to that indicated by the results of the thermal and X-ray diffraction analyses. The degree of vitrification of the fired bodies was further proof of their reactivity. This article is referencing the effects on clay in a gas kiln: not glazes. Citing the absence of oxygen in the kiln environment actually caused the clay body to experience a higher degree of fluidity (liquid phases) resulting in a higher degree of vitrification. More specifically, mullite and corderite formations: both refractory materials. Can anyone who fires in both electric and gas kilns testify to the differences in density or vitrification? Found the conclusions and commentaries in this article interesting. Nerd In which issue was this CI article published? I would like to read it before making significant comments. LT Link to comment Share on other sites More sharing options...
oldlady Posted March 22, 2016 Report Share Posted March 22, 2016 in a current post titled something like "finding your work in a thrift shop", there is a photo of a cup made years ago by mark. if you look at the bottom you can see that the clay is completely clean, is that the result of actual vitrification? i know the fired white cone 6 stoneware clay i use gets dirty and i know it is not vitrified. somehow the tightness of the porcelain in mark's cup has prevented the dirt buildup. this is the kind of question an education would have answered, i think. Link to comment Share on other sites More sharing options...
timbo_heff Posted March 22, 2016 Report Share Posted March 22, 2016 Since FeO is a flux on silica, if the kiln is fired in reduction, and the reduction occurs when the body is still gas permeable to the CO molecule, AND there is some level of Fe2O3 present, then the added flux would likely produce a more fluid melt. This impact might be what they are talking about. Heavily iron fluxed glass in a body can promote brittleness... so generally too much is not a good thing even though it can decrease Apparent Pororsity figures.....so I can't believe that they are talking about that kind of level. Never tested the two directly against each other for something like MOR. (same body in electric and reduction gas) best, ................john Have heard anecdotal evidence of this.... Thanks JB for knowing that it's correct and also why ! .... you are the best! Link to comment Share on other sites More sharing options...
neilestrick Posted March 22, 2016 Report Share Posted March 22, 2016 Where does is say 'absence of oxygen'? If they were indeed testing oxidation vs reduction, then it's definitely apples to oranges and this test means nothing. Link to comment Share on other sites More sharing options...
glazenerd Posted March 23, 2016 Author Report Share Posted March 23, 2016 Think I might have figured it out... maybe.. big maybe? Achieving Self-Glazed Porcelain Bodies- Oct 1, 2006 in the Ceramic Industry mag. These porcelain bodies were fired at 1300C in an oxidizing gas kiln environment. Alluded to what John said: the oxides came to the surface of the pieces to form a self sealing glaze. Also mentioned cordierite formation: which seems to be the one key to complete vitrification. The article mentioned above came out the same year; must have been a hot topic that year. Going to assume at this point that cone 10+ produces results that cannot be achieved any other way. Dr. Dipl. Eng. Aurica Goleanu is chief of the technical laboratory department at S.C. Apulum S.A., a company that manufactures porcelain products. . << argue with her Neil.. In another article, confirmation of what I have suspected and preached for years: "Unfortunately, potters buy less than 1/10% of all mined clays, so they have very little influence on the quality of the clays that are supplied. As long as fireclays meet or exceed the major user industry's requirements (and they currently do, even with all of their impurities), potters and ceramic supply companies do not have the economic purchasing power to demand a better grade of fireclay from the mines." .Then we wonder why our clay and glaze have frequent problems. Nerd Link to comment Share on other sites More sharing options...
neilestrick Posted March 23, 2016 Report Share Posted March 23, 2016 Now I'm really confused. So this has to do with self-glazing bodies, not typical ceramics? And I though it was about electric vs gas, not cone 10 vs. cone whatever? Link to comment Share on other sites More sharing options...
glazenerd Posted March 23, 2016 Author Report Share Posted March 23, 2016 Sorry Neil: was sort of answering my own question with yet another article I found. Next topic. Nerd Link to comment Share on other sites More sharing options...
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