Natania Posted November 22, 2013 Report Share Posted November 22, 2013 Attached is a picture of something that keeps happening in my kiln. It only affects 1-2 pieces per firing, but it is getting tiresome. Can anyone tell me what it is? It is like a chalky / salty textured blemish that is dry and crusty looking. Any thoughts would be extremely helpful since I lost two pieces that I needed for an order to this menace! Link to comment Share on other sites More sharing options...
neilestrick Posted November 22, 2013 Report Share Posted November 22, 2013 What clay body? Is it always on the same glazes? What cone? What firing schedule? Is that a black clay body? Those can do all sorts of funky thing to glazes. Link to comment Share on other sites More sharing options...
Natania Posted November 23, 2013 Author Report Share Posted November 23, 2013 Sorry, Neil. It is a Standard 266 clay body with a "white" cone 6 glaze that I apply thinly to get that reddish sienna-brown effect. Norm, do you think that slower cooling will help stop or reduce this problem? It only happens to a few pieces now and again, as you mentioned, but not knowing which ones will bite the dust is a bummer! I'll also have a look at my glaze recipe, but it would be easier for me to slow-cool than to change the glaze recipe.... Link to comment Share on other sites More sharing options...
neilestrick Posted November 23, 2013 Report Share Posted November 23, 2013 Sorry, Neil. It is a Standard 266 clay body with a "white" cone 6 glaze that I apply thinly to get that reddish sienna-brown effect. Norm, do you think that slower cooling will help stop or reduce this problem? It only happens to a few pieces now and again, as you mentioned, but not knowing which ones will bite the dust is a bummer! I'll also have a look at my glaze recipe, but it would be easier for me to slow-cool than to change the glaze recipe.... The problem is the clay. Many, many glazes react unfavorably on the Standard 266. There are only a couple in of glazes in my studio that work well on that clay. Additionally, that clay is really only stable at cone 5. It often bloats at 6, so you may be on the edge there, and that could be causing the glaze issue as the body gasses out. Link to comment Share on other sites More sharing options...
Benzine Posted November 23, 2013 Report Share Posted November 23, 2013 That's a nice glaze Norm. I looks like a lighter version of a Amaco Jewel Brown glaze, I use in my classroom. Link to comment Share on other sites More sharing options...
Benzine Posted November 23, 2013 Report Share Posted November 23, 2013 Once again Norm, very nice. My classroom glaze is actually a 05 glaze. But the "sparkle" effects really only show up, if you put three GOOD coats on. The bottle only calls for two. I probably use more than the students, because they think it just a maroon color. Then they see how it turns out on my items, especially layered with some other of my favorite glazes, then they want to use it. Link to comment Share on other sites More sharing options...
Benzine Posted November 23, 2013 Report Share Posted November 23, 2013 Since I'm pretty sure this is the formula, you could easily take commercial Jewel Brown and flux it up to Cone 6 by adding 10% silica (flint). This assumes commercial Jewel Brown in a pint is 50% water by weight, which usually just about right. Once again Norm, very nice. My classroom glaze is actually a 05 glaze. But the "sparkle" effects really only show up, if you put three GOOD coats on. The bottle only calls for two. I probably use more than the students, because they think it just a maroon color. Then they see how it turns out on my items, especially layered with some other of my favorite glazes, then they want to use it. I'll leave the glaze making, to you "Wizards" for the time being.... Link to comment Share on other sites More sharing options...
neilestrick Posted November 23, 2013 Report Share Posted November 23, 2013 I agree about crazy clay bodies. We typically use the Standard #266 unglazed, maybe with just a liner. It's a beautiful black, and takes very fine texture extremely well. While I do see your point, I would not consider Half-and Half to be a reactive clay. It's just half stoneware half porcelain, with nothing unusual in it that would cause problems with most glazes, whereas Standard #266 is ridiculously high in iron, plus has added manganese. So while the Half-and-Half does not work with your frit glaze, I respectfully propose that your glaze is the source of the issue. I think any good glaze should work on any 'normal' clay body without serious issues. I am all for glaze experimentation, but because I am only going to spend time testing glazes that I hope to one day put into my production work, or that my students will be using, I do have a couple of rules that I follow when formulating glazes. I know this takes some of the fun out of glaze testing, but these rules have saved me a lot of time and headache, and made for some wonderful glazes that are easy to use. And ease of use is key in my studio, for both myself and my students, as it save me a lot of time and keeps them happy. And I am in no way saying you are doing things wrong. With all things in clay, there are a million approaches. I just wanted to let you know my approach to glaze formulation, and possibly give you some ideas. First, I try to avoid glazes that have an overwhelming percentage of any one material, with the exception of simple low fire glazes. 90% 3124, 10% EPK is a classic cone 04 clear, because at low fire temps frits are quite stable for the most part. But when using high percentages of frits at mid-range temperatures, they are much less stable. I have also found that when using boron frits at cone 5/6, they generally need a lot more alumina and silica to stabilize them than you'd think. I have several glazes with 20% or more clay in them due to their high (30-40%) boron frit content. I have tested a lot of cone 6 glaze recipes from numerous sources, even published, that did not have enough clay or silica in them to truly be stable. Another other rule is that I generally shoot for at least 10% clay (koalin or otherwise) in my recipes. It keeps them suspended well, makes them apply more evenly, and makes the raw glaze surface more durable and easier to handle when loading the kiln. Without these properties I am wasting time every time I use the glaze, or my students are struggling to get them to work properly. Lastly, and similar to rule #1, I tend to avoid glazes that contain ingredients well beyond their typically used quantities. Again, you're asking for stability issues. So, given my rules, your Jewel Brown at cone 6 totally freaks me out! Tons of frit, high in iron oxide, almost no clay. Have you ever added 10% EPK to it? Or maybe replace some of the frit with neph sye? Just throwing out some ideas. Link to comment Share on other sites More sharing options...
neilestrick Posted November 23, 2013 Report Share Posted November 23, 2013 Frits are often a complete glaze, which need to be suspended with gum to avoid disrupting their chemistry. I use Xanthan gum and bleach Yes, but usually at low fire temps. And the application of a pure frit, even suspended, is kinda hideous to me. It's too powdery and weak, even with gum. Link to comment Share on other sites More sharing options...
neilestrick Posted November 23, 2013 Report Share Posted November 23, 2013 Ferro Frit 3195, a complete low-fire clear glaze, is I believe is roughly about the same as 70% Ferro Frit 3134 with 30% EPK, which has the advantage of being self-suspended. I think you'll find this 70/30 recipe stable at cone 6. Given my rules, your Jewel Brown at cone 6 totally freaks me out! Tons of frit, high in iron oxide, almost no clay. Have you ever added 10% EPK to it? Or maybe replace some of the frit. with neph sye? How can it be stable at cone 6 if it's a complete low fire glaze? It's either underfired at one or overfired at the other. Link to comment Share on other sites More sharing options...
Benzine Posted November 24, 2013 Report Share Posted November 24, 2013 Like I said....Wizardry. Link to comment Share on other sites More sharing options...
Natania Posted November 24, 2013 Author Report Share Posted November 24, 2013 The weird think is that the clouding (or whatever it is) happens on my laguna B-mix 5 also - also with the white glaze. And on the standard 266 once with a different glaze. So not sure what is up. I've never had this happen in other kilns...I fire the 266 to cone 5 and may try a cone 4 because my kiln fires a bit hot anyway. Thanks for everyone's input and other interesting glaze info. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.