Rex Johnson Posted September 8, 2015 Report Share Posted September 8, 2015 Evidently I've had a senior moment. It's been a while since I used RIO and Cobalt Oxide for brush decoration, maybe a couple years. At any rate my RIO seems fine just mixed with water. But my Cobalt Oxide isn't staying mixed, it just falls to the bottom, and in an hour separates and falls to the bottom of the jar into a hard silt. What am I doing wrong? Should I add some clay or bentonite? Link to comment Share on other sites More sharing options...
Mark C. Posted September 8, 2015 Report Share Posted September 8, 2015 I use water with colbalt Carb-it settles out and I just mix it with the brush again. Mark Link to comment Share on other sites More sharing options...
Rex Johnson Posted September 8, 2015 Author Report Share Posted September 8, 2015 I'm reading about cobalt carb but never used it for brushing. Doesit come out the same dark blue? I use CO over or under white or clear. Yes, I do use the brush t mix and go but it seems to settle quicker than I remember. Ive also added Frit from as suggested atone other thread to make it flux better. Maybe the frit is making it settle quicker... This is an example of what I use cobalt for, simple bamboo brushing... Link to comment Share on other sites More sharing options...
Mark C. Posted September 8, 2015 Report Share Posted September 8, 2015 Oxide is twice as strong.Frit would flux it somewhat. Mark Link to comment Share on other sites More sharing options...
Cavy Fire Studios Posted September 8, 2015 Report Share Posted September 8, 2015 I use gerstley borate for my stains and oxides, and it works pretty dang well. I can't remember the ratio, though... I'd try one part cobalt, two parts gerstley borate. Although, I have a mason stain called Mazerine Blue that is VERY VERY cobalty (like, the powder is that weird pinkish color), and its ratio is 1:4... best make some test tiles. Link to comment Share on other sites More sharing options...
oldlady Posted September 8, 2015 Report Share Posted September 8, 2015 seth cardew does the kind of brushwork shown. at his workshop, he simply mixed a little cobalt carbonate with water and stirred it often. he did the same with RIO to get a second color. Link to comment Share on other sites More sharing options...
TJR Posted September 8, 2015 Report Share Posted September 8, 2015 If you add fritt to your cobalt it will be heavier and settle out quicker as fritt is ground glass. Ger.Bor. would be a better choice. You do have to stir it constantly. TJR. Link to comment Share on other sites More sharing options...
Rex Johnson Posted September 9, 2015 Author Report Share Posted September 9, 2015 Thanks folks, I'll give the GB a try. Link to comment Share on other sites More sharing options...
Joseph Fireborn Posted September 10, 2015 Report Share Posted September 10, 2015 I do 50RIO/50GB for my iron stain. It stays suspended pretty well for a few minutes but you do have to stir often, its just part of this type of mix I think. Link to comment Share on other sites More sharing options...
Guest JBaymore Posted September 10, 2015 Report Share Posted September 10, 2015 Rex, Man... your work there in the image looks a lot like Hamada Shoji's. Hamada's slightly grey-ed out blue there is based on something called gosu... which is an impure source of cobalt. The ground rock also contains a bit of manganese dioxide and iron oxide and some fluxing materials. The gosu is a very fine mesh material when used for this (as well as for overglaze enamel use). The finely ground gosu powder is typically blended with a thickened mixture of a green tea extract (make strong sencha type green tea from leaves, let it sit 'forever', then boil off some of the water) that lends it brushing consistency and acts as a kind of "fixative" when it is dry. For the following, note that I an working high fire.... cones 9 to 14. As far a the stuff I use here in the US, I also use cobalt carbonate as the starting point of a mix rather than cobalt oxide. Typically the carb form is a finer particle than the oxide from US suppliers. Then to that I add a small amount of Cedar Heights Redart to add a trace of iron into the color mix, to supply a bit of flux, and to also enhance the suspension and brushability in the wet state. Then comes a pinch of manganese dioxide for the color rendition (takes the "harsh" out of straight cobalt compounds). Then a tiny bit of frit 3124 as more flux. Add water. Then I also add some glycerin to make it all brush better. For the stuff that gets brushed on top over a raw glaze coating, I also add a tiny bit of white wood glue. This causes the "dust" to set when dry and not get smudged in handling when stacking. White wood glue burns right off and leaves no trace. If you do this you have to keep the material in a covered container when not in use. If you try this kind of mixture, to get the ratios of the coloring sources correct, you'll have to test to your own tastes in the blue you want to achieve. best, ................john Link to comment Share on other sites More sharing options...
Rex Johnson Posted September 10, 2015 Author Report Share Posted September 10, 2015 Thanks John, Yes that is a borrowed image. Funny I couldn't find exactly what I was looking for I have some pieces at home that are brushed over a clear cone 10 glaze that are very succesful/ I'll try and remember to take a pic. I suspect having read adding flint may be the culprit as suggested. It's completely (and quickly) separated in the jar. This is probably a better example (borrowed ; ) ) .... Link to comment Share on other sites More sharing options...
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