redbourn Posted December 10, 2016 Report Share Posted December 10, 2016 I recently made and used Mary Barringer's cone 6 redact slip recipe (Spodume 10% Cedar Heights Redart 80% Lithium Carbonate 10% add 2% red iron oxide). I glazed with a Spectrum satin clear glaze. In the glaze firing the slip turned a very nasty dark brown. Any ideas why this happened? Link to comment Share on other sites More sharing options...
neilestrick Posted December 10, 2016 Report Share Posted December 10, 2016 What color is is supposed to be? With that much Redart and iron I would expect it to be a dark brown. Link to comment Share on other sites More sharing options...
bciskepottery Posted December 10, 2016 Report Share Posted December 10, 2016 Might it be a reaction between the slip and the clear glaze? Does she fire oxidation or reduction -- that could make a difference. From pictures, she seems to use only the slip/engobes on surfaces with no covering glaze, and letting the kiln atmosphere do its work. Link to comment Share on other sites More sharing options...
redbourn Posted December 11, 2016 Author Report Share Posted December 11, 2016 Thanks to Neil and bciskepottery. I believe she fires in oxidation. Neil, I'm new to all this and so thought the lovely red of the slip would remain. Sounds like I'm wrong. Link to comment Share on other sites More sharing options...
Magnolia Mud Research Posted December 12, 2016 Report Share Posted December 12, 2016 I use redart clay mixed with a tad of baking soda on raw clay; also without the baking soda. Applied to green ware at the leather hard or bone dry state, and to bisque ware. On bisque ware, the application must be thin until it dries, or the shrinkage will cause it to flake off. Multiple coats is the way to build up the thickness. My work is usually fired to cone 10 in a gas kiln with mild reduction. If the redart is under a glaze, the glaze will significantly change the character and color of the fired marks. If the redart marks are left bare, then the redart usually fuses to the substrate and is red to brown depending on where in the kiln and the local oxygen fugacity. My latest adventure rendered the marks as an dark orange-red color. The color also depends on the composition of the underlying clay body. A dark burning stoneware will be react differently than a very white porcelain. Part of the difference will be due to the contrast between light and dark, and partly due to the reactions between the redart and the substrate composition. At cone 5 electric I would expect it to be a nice red. LT Link to comment Share on other sites More sharing options...
preeta Posted December 12, 2016 Report Share Posted December 12, 2016 i am not sure which RIO engobe we use. seems like similar recipe. even our test tile shows under glaze the engobe turns a dark brown. actually any form of iron under clear glaze changes in oxidation. if i put RIO on my bisqueware and then apply clear glaze on it, nothing or very little of the RIO will remain on the pot. but if i put RIO on top of clear the colours remain. Link to comment Share on other sites More sharing options...
redbourn Posted December 12, 2016 Author Report Share Posted December 12, 2016 "actually any form of iron under clear glaze changes in oxidation. if i put RIO on my bisqueware and then apply clear glaze on it, nothing or very little of the RIO will remain on the pot. but if i put RIO on top of clear the colours remain. " Very interesting. Thank you. --redbourn Link to comment Share on other sites More sharing options...
neilestrick Posted December 12, 2016 Report Share Posted December 12, 2016 i am not sure which RIO engobe we use. seems like similar recipe. even our test tile shows under glaze the engobe turns a dark brown. actually any form of iron under clear glaze changes in oxidation. if i put RIO on my bisqueware and then apply clear glaze on it, nothing or very little of the RIO will remain on the pot. but if i put RIO on top of clear the colours remain. It all depends on how much iron there is in the engobe/underglaze, and how thick the iron is applied. Link to comment Share on other sites More sharing options...
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