Afranklor Posted February 11, 2016 Report Share Posted February 11, 2016 I seeking a clear glaze for cone 6 that does not neutralize a red iron oxide stain. I have tried a few and they all neutralize (make invisible) the red iron oxide. I am new to ceramics so please forgive me if I am not using the right terms or if this is an ignorant question. I have tried several glazes (including a zinc free) and they all erase the iron oxide and just show the speckled buff beneath. If you have had success with a clear glaze( for cone 6) over a red iron oxide stain please let me know. Link to comment Share on other sites More sharing options...
MatthewV Posted February 11, 2016 Report Share Posted February 11, 2016 Iron oxide will turn brown/black in the ∆6 firing range. If it isn't showing up it is because it hasn't been applied thick enough. This was with a celadon instead of a clear but green hue aside, the iron will behave the same: ∆6 oxidation firing Link to comment Share on other sites More sharing options...
Joseph Fireborn Posted February 11, 2016 Report Share Posted February 11, 2016 Welcome to the boards. What is your iron stain recipe? I would lean towards that being more the issue than the actual clear. Either your application is too thin as Matthew stated above, or your stain has a lot of frit and not very much RIO in it, which is causing it to melt into the clear and be very faint. It could be something else, but I haven't ever had this problem and I used to work with a lot of iron stain brush marks, under and on top of a clear. A quick test would to take a tile and push several layers of brush marks on it in different thicknesses and fire it and see if any of them show up. This way your not ruining good work. Then also make up some other iron stain recipes and do the same thing. I use this one : 50 Gerstley Borate 50 RIO(Synthetic) I prefer it over the ones with more frit and lower RIO. Link to comment Share on other sites More sharing options...
Afranklor Posted February 11, 2016 Author Report Share Posted February 11, 2016 Thanks for this feedback but the RIO is not the issue. I stain the entire exterior of the mug with the iron oxide stain which turns a wonderful deep red brown. I am leaving the bulk of the exterior of the mug glaze-less (ie just the iron oxide stain) then adding a clear glaze over the oxide at the lip and interior to make the mug food safe. The result of the clear glazes I have tried is a stark line where the oxide meets the clear glaze. Underneath the clear glaze there is no red iron stain, instead the lightness of the speckled buff clay body is visible as if there were no iron oxide used. The stain being used is RIO, water and a pinch of epsom salt. Thanks again for any feedback you can offer! Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted February 11, 2016 Report Share Posted February 11, 2016 I have to agree with Matthew there is not enough red iron oxide. The iron speckles are making it through the glaze without disappearing so I think the amount you are using is being taken in by the glaze. Link to comment Share on other sites More sharing options...
MatthewV Posted February 11, 2016 Report Share Posted February 11, 2016 I've always used china clay instead of a flux with my oxides. For iron about a 50-50 works well; I won't even pretend I measure. I also work in a way where I wish to keep brush stokes an different thicknesses visible. Afranklor-- if you are happy with the unglazed portion of you piece, learn to be happy with the glazed lip. No glaze will darken with the trace of iron you are applying. Link to comment Share on other sites More sharing options...
bciskepottery Posted February 12, 2016 Report Share Posted February 12, 2016 As long as you glaze the inside and the top of the rim you should be okay. No need to bring the glaze over the rim and on the outside. Iron is not toxic and unless you lick the dribbles down the front of your mug, the outside being glazeless should not make a difference. Link to comment Share on other sites More sharing options...
PeterH Posted February 12, 2016 Report Share Posted February 12, 2016 If you are going to do some test tiles, you might try a soda wash on one to see how it looks. http://community.ceramicartsdaily.org/topic/6933-soda-ash-wash-and-electric-firing/?hl=%2Bsoda+%2Bwash Motivation. This is using soda wash as a proxy for a glaze that doesn't dissolve iron (e.g. Ca-free? [1]). [1] Geysbeek, Red Glazes at high temperatures Transactions of the American Ceramic Society, v1, pp 62-65 (1899) Which is on pages 68-71 of the scanned copy at: https://ia600302.us.archive.org/27/items/transactio01amer/transactio01amer.pdf A transparent version of these c8 gazes might be brought down c6 by adding boron. But how do you get a calcium-free insoluble source of boron (without making your own frit)? Link to comment Share on other sites More sharing options...
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