Bob Coyle Posted March 7, 2014 Report Share Posted March 7, 2014 This glaze was taken from Glazes Cone 6 by M Bailey and modified. It breaks blue where thick on clays containing iron. Really pretty on Laguna speckled buff.Glaze test on Laguna clay bodies. Fired up to cone 5 with kiln setter shut off. 125 F/hr from 1700F to shutoff.Comp %Neph Sy 68G.Borate 08Ball Clay 08Whiting 05Silica 04Rutile 02Titanium 02Cobalt Carb 01 Link to comment Share on other sites More sharing options...
neilestrick Posted March 7, 2014 Report Share Posted March 7, 2014 The color is great, but I would definitely check it for durability and leaching. The sodium is off the charts in the limit formula, the alumina is pretty high, and that's a lot of cobalt. If you look closely at your tiles you're getting a lot of rough, pitted areas which aren't great for functional wares and signal that something is wrong in the glaze. Of course, all of these things are probably what's contributing to the great color, so you'll have to decide what's important. It would be worth testing some variations on this glaze to see if you can get the numbers within limits and still retain the color. Link to comment Share on other sites More sharing options...
Bob Coyle Posted March 7, 2014 Author Report Share Posted March 7, 2014 Neil The leeching is no problem. All of my glazes soak for 2- 4 days in a plating bath containing a strong solution of sulfuric acid. If they survive this they will probably be OK with tomato juice. Also none of this is used for dinner ware, although I don't think anyone would get poisoned by using it on a mug. The rough pitted areas are kind of a "feature". They have a tendency to level out with more of a soak. The glaze is right on the edge of being under fluxed. At cone 6 it is smoother and shinier but more blue with less break. I like the more rough matte surfaces and try for this look on most of my glazes. The proportions are really not that far off from those in M Bailey's book. His examples were all functional potter. Link to comment Share on other sites More sharing options...
neilestrick Posted March 7, 2014 Report Share Posted March 7, 2014 Good to know you've checked it out. And for non-dinnerware items there's not an issue, anyway. Link to comment Share on other sites More sharing options...
Bob Coyle Posted March 8, 2014 Author Report Share Posted March 8, 2014 Yeah Neil, I keep forgetting to say my glazes are not tested for being food safe. Here is what it looks like on an electroformed piece. As I said I like the kind of matte "old" look Link to comment Share on other sites More sharing options...
Babs Posted March 8, 2014 Report Share Posted March 8, 2014 Beautiful effect Bob, i love the breaking. Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted March 8, 2014 Report Share Posted March 8, 2014 What charts are these? I have no charts that tell me things like this Beautiful glaze, would love to see one of your mugs with it on. Link to comment Share on other sites More sharing options...
Babs Posted March 8, 2014 Report Share Posted March 8, 2014 What charts are these? I have no charts that tell me things like this Beautiful glaze, would love to see one of your mugs with it on. Oh you are way too literal up there! And they are not the music charts!! Spring will come soon and all will be revealed! Link to comment Share on other sites More sharing options...
neilestrick Posted March 8, 2014 Report Share Posted March 8, 2014 What charts are these? I have no charts that tell me things like this Beautiful glaze, would love to see one of your mugs with it on. Glaze formula limit charts. They show the acceptable limits for each part of a glaze in the unity formula. If the numbers are within the limits, then a glaze is more likely to perform well. There are, of course, perfectly good glazes that have numbers outside these limits, but they are a good place to start, and can show you where to make adjustments if the glaze is having problems. http://digitalfire.com/4sight/education/limit_formulas_and_target_formulas_206.html Link to comment Share on other sites More sharing options...
Babs Posted March 8, 2014 Report Share Posted March 8, 2014 Didn't have to wait till spring with Neil on board. Thanks Neil. ( Again) I stir up High Gate to keep him/her awake at work! Link to comment Share on other sites More sharing options...
Dick White Posted March 12, 2014 Report Share Posted March 12, 2014 The cobalt green effect in that glaze is due to the titanium (from the rutile) and the high level of alumina. Same effect as in the ^10 Reitz Green glaze. Because the high alumina is necessary for developing the green color, you probably won't be able to smooth out the surface by adjusting the glaze to a higher Si:Al ratio. Interesting adjustment you made there by substituting additional Gerstley for the spodumene. You effectively changed out the lithium flux (from the spod) for twice the boron (from the additional Gerstley). Link to comment Share on other sites More sharing options...
Bob Coyle Posted March 12, 2014 Author Report Share Posted March 12, 2014 Interesting adjustment you made there by substituting additional Gerstley for the spodumene. You effectively changed out the lithium flux (from the spod) for twice the boron (from the additional Gerstley). That is correct Dick. I didn't have any spod at the time and tried an adjustment with Li Carb and upping the ball clay. I had a ton of G borate so I tried that as a flux instead and it worked out OK. I added extra TiO2 to opaque it more. I am trying for a more antique look and the roughness is fine. Firing at cone 6 will smooth out the bumps but produces more gloss with some loss of the green break. The green break also depends on the clay body. Works on darker stoneware bodies. Link to comment Share on other sites More sharing options...
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