Beebop
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Posts posted by Beebop
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If a glaze sources all its Al and Si from feldspar and does not contain clay, will bone ash still cause over-flocculation? I am assuming it’s the interaction of P+ with the clay particles that causes it, just wondering if eliminating clay is a possible route to avoiding gelling in the bucket for bone ash glazes. Or will this just lead to hardpanning? Thanks!
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4 hours ago, Min said:
If you do use either Magma or CMC be sure to add a tiny amount of copper carb to act as a preservative, it will work with either.Do you think copper oxide be substituted for this purpose?
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On 7/28/2022 at 12:43 PM, Mark C. said:
Another Magma vote -it cures all settling issues with a very small amount needed.It can float a brick
I added a new post with follow up questions. I’m very intrigued by this solution!
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On 7/28/2022 at 10:32 PM, ATauer said:
I don’t think you should look at it as an all or nothing issue, such as replacing all your EPK with ball clay. There are plenty of recipes out there with ball clay instead of or with EPK, it depends on the requirements of the glaze. Depending on how the glaze was developed, there may have been (hopefully there was) extensive testing with multiple line blends or quadraxial blends to determine which of the possible glazes had the most desirable characteristics and that determined the recipe. I’m aware plenty of recipes seem to be just thrown together or are alterations of other recipes, or blending of two recipes (which is such fun to try! You never know what you might end up with!). So hopefully some thought was put into which clay was used, generally the determination should have a lot to do with how much silica and alumina you want and you can adjust that with ball clay without necessarily changing how much flint or feldspar is added. I will say the recipes I see ball clay in I honestly can’t work out usually why they are using it. But your problems that you are having, are not typical of EPK except of course at high enough levels to have excess shrinkage and need calcining. But that doesn’t always solve things, and it may not be your solution. I wouldn’t just jump to trying ball clays instead in these recipes, you’d have to alter the recipes with glaze calc software and people forget that ball clays have an extremely high shrinkage rate themselves, so I don’t know that it would solve your issues. Especially looking over the recipes you shared, the levels of EPK are quite moderate, no where near I would be concerned or recommend calcining. I would be looking elswhere. Any new bags of materials you’ve bought in the last couple of months? Switch to a new supplier? Are you using a newer talc?
The other thing I wanted to add is if you haven’t tried CMC with these recipes I would give it a good shot. It will significantly improve the bond between the bisque and the glaze, it literally helps it stick on harder, and tends to help with glazes that are problematic at this stage- we literally use it as a glue in glass fusing and apparently most wallpaper pastes are made out of it! It should help with preventing dried glaze cracks and allow for a smoother application and I think that will maybe help with the crawling. Of course with crawling there are all the typical things about making sure the bisque is super clean, no dust, no fingermarks, no grease to cause the glaze to crawl. It might well help a lot to do a quick dip in water before glazing, that often helps with crawling. I just think looking at your recipes the crawling is not coming form the EPK at all, there just isn’t enough of it to be the problem, so the detective work should shift in new directions. And considering you are having problems with so many glazes…that’s weird. I’m really wondering about any materials you’ve replaced recently. I could see this happening on one or two glazes but not this many unless a material is contaminated…
This is very helpful, thanks for the feedback. I’ve only been making glazes for a couple years now and haven’t had to rebuy anything yet except talc, which involved switching to Texas talc from another one that is no longer sourced, though I haven’t noticed much of a difference in performance. But now that I’m saying that I should go back and actually look at my recipes and results to see if there’s a correlation. It’s not that all my glazes have the same problem, but that most of my glazes have some problem, many of them being hard panning, pin-holing, crawling, cracking when dry, glaze fail caused by layering. I think a big part of my problem is that I need to work with a lower SG, and I have some other fixes I’m working on as well, though trial and error is slow when you do glaze firings at most every other month! I am definitely interested in using an additive I think that could go a long way for me in problem solving, added a new post with follow-up questions on that. Thanks!
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I have follow-up questions based in recommendations from my previous post. I’m looking into MAGMA and CMC additives to improve the working properties for some of my glazes. I see that both thicken a glaze. Since the glaze+additive goes on thicker, does this cause a thicker glaze layers in the fired product? Or is the thickness entirely due to the organic that burns off, and it leaves behind roughly the same amount of glaze after firing? Should I be trying to dip quicker or brush fewer layers since the glaze is thicker, or apply as normal because glaze thickness is just not the equivalent when compared to a glaze without additive? Thanks the all the help, I learn so much each time I post I really don’t think I could be a glaze maker without this forum!
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10 hours ago, Min said:
If these were my glazes I would calcine some of the kaolin in the first recipe. For the ones with bone ash, I'm wondering if the bone ash (real or tricalcium phosphate?) is gelling the glaze and tricking you into adding more water which in turn would cause more shrinkage as the raw glaze dries causing the crawling. Have you tried different SG's of those ones and seeing if raising it reduces the problem? Worst case scenario I would get some Magma (Brackers sells it) and add a small amount of it to those bone ash glazes. (Magma needs to be made into a jell then a small amount of that is added to glazes. It helps stop glaze cracking and crawling but does slow down the drying time. It is also a great floc.)
I have never heard of Magma but just looked it up and it sounds like a miracle! I will definitely give this a go! I have run into some really impressive problems with bone ash gelling, but this particularly one rendition has been ok. I’m still learning when something needs more/less water versus floc/defloc though.
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5 hours ago, Bill Kielb said:
Just a comment here, crawling can often be the result of the fired glaze surface tension preventing its ability to heal so cracks developed early on can exacerbate the issue. Calcining part of the epk often can help with the shrinkage and help with the early formation of cracks. Interestingly ball clay is know to shrink more, but does not necessarily translate to more early formed cracks maybe because it is more plastic or has a more favorable fired glaze surface tension or both so you might have an idea worth testing.
That’s very compelling and makes a lot of sense. I’ll definitely give that a go. Thanks!
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16 hours ago, Min said:
Ball clays are of much smaller particle size than kaolins. On the other hand kaolins are whiter and cleaner burning than ball clays. Smaller the particle size the more plastic a clay will be, this means that if you use a ball clay in place of a kaolin then bentonite might not be necessary to achieve the same level of glaze suspension. Glazes with significant amounts of clay will need to have some of the clay calcined to reduce shrinkage of the raw glaze which otherwise could precipitate the glaze cracking upon drying. If your glazes are up around the 20% clay amount I would rebalance the silica and alumina in the recipes if swapping from one to the other. I use both OM4 and C&C ball clays for glazes but for the most part use EPK and bentonite where necessary, usually if the glaze has less than around 15% EPK in them.
Good advice, I will work on sourcing silica and alumina elsewhere or calcining clay for problemtic recipes with high clay content. Thanks for the suggestions!
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16 hours ago, Bill Kielb said:
Thanks for posting them, Just a question: do they ALL exhibit issues or are one or two of the above worse than the others?
Good question. I have lots of kinks to work out in general, some are better than others. The first and the third one I posted (CGB2 from Hesselberth and Roy and a SiC-Jun in test/development phase) are two of the most problematic as far as crawling on the finished product. The fourth one cracks a lot on drying but rarely crawls, been trying out different EPK levels on that one from 0% to 20% to limit running. The second one is a kaki I’ve been developing, it rarely has issues with application or final defects.
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I’m less asking about how to fix those specific defects and more wondering if there’s a benefit to using ball clay instead of EPK. I added screen shot of some recipes I use, usually EPK below 20% and bentonite at 2%. Thanks!
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I use EPK in my glazes usually with a bit of bentonite, I don’t have any non-bentonite ball clay on the shelf. But should I? Would ball clay have better working properties for a glaze than EPK+bentonite? If ball clay is a must on the ingredient shelf, why and which one do you recommend? I seem to have issues with suspension and cracking/lifting during drying, not sure if that could be improved with a different clay. Sort of assume not but I’ve never used ball clay before so idk. Looking to place a materials order so if I were to try some, now is the time. Thanks!
Does bone ash still flocculate without clay?
in Clay and Glaze Chemistry
Posted
Ok good advice. Thanks!