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Clear Glaze Chemistry


amoqt

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Gerstley typically runs 27 percent boron, and colemanite can run well over 40 percent. I use calcium borate on a fairly regular basis, little does a lot.

 

Amoqt: perhaps a list of available materials will help with an answer. You do have another option, which is more heat. Run a series of tests a cone higher than you currently use. Then two cones higher. Porcelain can tolerate a fair amount of heat.

 

Nerd

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Gerstley typically runs 27 percent boron, and colemanite can run well over 40 percent. I use calcium borate on a fairly regular basis, little does a lot.

 

Amoqt: perhaps a list of available materials will help with an answer. You do have another option, which is more heat. Run a series of tests a cone higher than you currently use. Then two cones higher. Porcelain can tolerate a fair amount of heat.

 

Nerd

 

Hi Tom,

Amoqt did list his supply of ingredients, "feldspar, whiting, borax, dolomite, talc, silica and kaolin", and he is using a semi-porcelain / stoneware type clay. Unless he goes to the cone 10 range I can't see how he is going to make a decent glaze without some kind of insoluble boron. Think it's like trying to frame a house with no nails.

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RonSa I'll check if it's possible to buy any of that, thank you. The main problem is companies sell these products in tons and roughly milled for major manufactors of ceramic tiles and such. But what the hell, I'll directly ask them. Thank you for pushing me to solving this. For now I buy from sellers that supply ceramic artists and it's not common here to make glazes instead of buying commercial ones. So I can't even ask for advice from locals. -__- glazenerd that clay has a firing range up to 6 cone, the higher it gets the more fragile. Also my kiln is not suitable for going that hot. I made that kiln specially for 1200-1230 range. I didn't have money to buy branded kiln, but I wanted to start so badly that was agree to anything, haha :) I hope to long for a few years until I make a better kiln for a higher temperature. 

I've found fine nepheline syenite (norwegian). For the moment I bought materials it was not available, but it is now. I'll buy next month.  

Min thank you for understanding my situation. I'll get another materials in next month. I'll post my progress and recipes here.

Thank you all guys I realized my problem.

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The "problem" with barium carbonate is that having it in your waste stream = toxic waste according to current EPA rules.  It's not *that* toxic to humans as you noted, but problematic for fish and aquatic life forms.  It is one of the things we voluntarily removed from the studio where I work in order to simplify disposal of glaze waste, spray booth filters, etc.  It also meant that we don't have to worry if a careless student washes it down the drain.  Some things are great, and make beautiful glazes, but we simply don't need the headache of dealing with them in an educational setting.



 " one of my favorites contains barium carbonate which many potters refuse to have in their studio.

 

if i researched it correctly, the fear comes from the fact that it is used as rat poison.  history shows some really strange mistakes.  someone used it in place of flour in cooking for group of soldiers(?) and poisoned them.  they all recovered but the fear is strong.  i cannot imagine a potter trying to cook with ANY ingredient from the studio.  so after finding no fatalities online, except for a suicide, i decided i could use the small percentage of barium carb the recipe calls for.  it also goes over green underglaze without changing the color to grey, a big deal for me."

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thank you for clarifying the reason for caution.  my recipe calls for 8% barium.  i am on the potomac river, above the junction of the shenandoah and potomac.  i do worry about the creatures in the river but i truly cannot see that tiny bit of unrecovered overspray as harmful, i reclaim a lot of glaze and re-use it.  what escapes has a long way to get to the water itself, i think it winds up in the soil which is mostly red clay.

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Our concern at work was students washing mixing buckets/tools/sprayers/mistakes... And dealing with disposal of the spray booth filters. Not using this one ingredient means that our filters are not considered "toxic/ hazardous waste" by the environmental regulators and our in-house risk management and safety people. Some folks are careless, so we have to set things up in ways for the least common denomenator at times. I'm surprised/not surprised by how much stuff ends up in the sink traps in such short order. There are ways one could deal with it, but the logistics headaches weren't worth it to us.

 

The liability differences between a single person running a tight ship, and an institution where people are encouraged to learn through their mistakes is very different.

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amoqt, if you are in your own studio, having a bucket of water inside the sink is a great idea.  that way, you wash off the heavy stuff inside the bucket.  letting it settle and keeping the contents until they dry out is one way to avoid a problem.

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Guest JBaymore

 

The "problem" with barium carbonate is that having it in your waste stream = toxic waste according to current EPA rules.  It's not *that* toxic to humans as you noted, but problematic for fish and aquatic life forms.  It is one of the things we voluntarily removed from the studio where I work in order to simplify disposal of glaze waste, spray booth filters, etc.  It also meant that we don't have to worry if a careless student washes it down the drain.  Some things are great, and make beautiful glazes, but we simply don't need the headache of dealing with them in an educational setting.

 

 " one of my favorites contains barium carbonate which many potters refuse to have in their studio.

 

if i researched it correctly, the fear comes from the fact that it is used as rat poison.  history shows some really strange mistakes.  someone used it in place of flour in cooking for group of soldiers(?) and poisoned them.  they all recovered but the fear is strong.  i cannot imagine a potter trying to cook with ANY ingredient from the studio.  so after finding no fatalities online, except for a suicide, i decided i could use the small percentage of barium carb the recipe calls for.  it also goes over green underglaze without changing the color to grey, a big deal for me."

 

 

This is exactly why I always stress that "education is a good thing" when it comes to the health and safety aspect of our field.  There is MUCH misinformation and "hysteria" in the ceramic community about various compounds and practices.  This is not to belittle that there ARE things that we should be concerned about.......... but to remind people to vet their sources, to go to primary sources whenever possible, to learn enough "science" so that you can understand the information at an appropriate level, and so on.  Those concepts are one core part of my ceramic toxicology sections I teach.

 

The "waste stream" business is an important one to be aware about for a large operation like a college ceramics program.  One issue there is that while the single ceramics department itself might fall under the 'small generator' exceptions in the laws, the college is typically looked at as a "whole".  So the wastes from the photo department, the ceramics department, the painting department, and so on all "count" toward the total tonnage/poundage that the institution produces on an annual basis.  Hazardous waste disposal fees are not trivial.

 

Yeah, I also believe that the "rat poison" aspect is what got the whole BC business started in the ceramics community.  A concern ... yes.  But people not really understanding what the "LD50" concept information for barium carbonate might imply helps to fuel a totally hysterical approach to the material.  Some places you'd swear it was radioactive plutonium we were talking about.

 

Then there's the craziness said on copper in glazes!  (Unless you have Wilson's Disease.)

 

Then there are the things that people SHOULD take far more seriously than they typically do.  The potential respirable microcrystalline silica issues from the ubiquitous "clay dust" that is REALLY prevalent in a studio situation, for example.  Diverse non-localized sources, large amounts of material in pretty constant use, hard to appropriately ventilate without huge costs for heated/cooled make-up air..... and so on.

 

 

The liability differences between a single person running a tight ship, and an institution where people are encouraged to learn through their mistakes is very different.

 

Very, very true.  And some of the "mistakes" can be whoppers.  ;)

 

best,

 

..................john

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Then there's the craziness said on copper in glazes!  (Unless you have Wilson's Disease.)

 

 

I'm pretty sure more copper leaches from the water pipes in my house than will leach out of most cups in ordinary use.   There are certainly exceptions, and obvious situations where one should be aware, though.   Dump enough copper in a glaze that does not get fired to maturity, and you end up with real potential problems, that one needs to inform end users about.  product liability is a thing we need to pay attention to, in some locales and countries more than others.  Europeans have pretty strict labeling requirements regarding items that are not compliant with basic food safety rules.

 

Then there are the foolish actions of the youth... I once made soup for lunch in the studio, and didn't have a bowl.  so I grabbed a copper bowl someone had made and used that.  Vomiting ensued in short order from the oxides and such that were still on the surface of the bowl after washing and had dissolved into my soup.  Lesson learned.  One must take precautions with things, and should follow best practices for safe glaze formulation, but paranoia is not necessary to the level that many people take it.

 

re: barium and other substances that are considered toxic waste, even a "small producer" of waste can have a relatively large effect on whomever or whatever is downstream from them.  While discouraging people from going overboard, too many people poo-poo and have a complete disregard for the impact that they have and take no precautions whatsoever.  Happy medium should be encouraged.  I like to encourage students with whom I discuss waste generation and other safety issues to be thoughtful and reasoned on the subject, as in all things.

 

 

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the problem those of us who learn on our own is that none of these considerations are emphasized in the usual ways we learn.   maybe someone with the proper knowledge could write a simple explanation of why it is ok for mother earth to have deposits of chemicals and minerals that have been here for millenia but potters pouring some of those things onto the earth or into a river is wrong.

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Guest JBaymore

I'm pretty sure more copper leaches from the water pipes in my house than will leach out of most cups in ordinary use.   There are certainly exceptions, and obvious situations where one should be aware, though.   Dump enough copper in a glaze that does not get fired to maturity, and you end up with real potential problems, that one needs to inform end users about.  product liability is a thing we need to pay attention to, in some locales and countries more than others.  Europeans have pretty strict labeling requirements regarding items that are not compliant with basic food safety rules.

 

Yup....... people seem to forget a LOT of houses have ...... COPPER pipes.  4% of copper oxide in a glaze batch that weighs 50 grams is on the inside of a mug....... that the water for the coffee or tea just came thru 100 pounds of copper pipes where maybe it sat since yesterday.

 

Any copper-bearing glaze that has the little black surface devitrification areas ("crystals") floating on the surface is absolutely not suited for food contact usage.  Copper compounds not well bound into glassy matrix and right on the surface.  Those glazes are beautiful.... and way off the mark on general "food safety" aspects.  Unfortunately, see them all the time on functional food pots.  Are they "death incarnate?  No.  But not good.  Back to the "good education" business. ;)

 

Anyone reading this thread that needs info on copper...... see the link Min posted above... I quote that one all the time.  As I've posted here many times...... Carty is " THE source" for good accurate glaze and toxicology info.

 

best,

 

....................john

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john, your post above, #41 came up only 7 minutes after i asked a question that you would be the perfect expert to answer.  and your post is at the top of a page so mine is in no-man's land.  please read it and try to explain it to all of us non-chemists, self-taught and without a degree.

 

i did read Min's post.  it was written for chemists who understand all of the abbreviations.  i found myself constantly referring back to the table where the chemicals were listed to see what Na or Ca or whatever else was mentioned was.  by the time i re-read the original sentence i had to consider much more than the original sentence.

 

your reference to the problems with copper ( i use copper carbonate ) is not explained for those of us without your extensive background.  the Carty article says only that a glossy glaze (which mine is) fired above cone 1 (i fire to cone 6) should not cause any problems.  IF i read it correctly.

 

yes, i should go to college and get a masters degree but i will not.  must i be excluded from the basic knowledge you are discussing?

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Then there are the foolish actions of the youth... I once made soup for lunch in the studio, and didn't have a bowl.  so I grabbed a copper bowl someone had made and used that.  Vomiting ensued in short order from the oxides and such that were still on the surface of the bowl after washing and had dissolved into my soup.  Lesson learned.  One must take precautions with things, and should follow best practices for safe glaze formulation, but paranoia is not necessary to the level that many people take it.

 

I guessing it may have been something else that might have made you sick. 

 

Copper bowls are a mainstay in whipping egg whites

The Science Behind Whipping Egg Whites in Copper Bowls

 

Copper bowls is also used for the preparation of caramelized sugar and honey in making candy.

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The copper bowls people use for egg whites and other culinary purposes tend to be clean of oxides.  Vomiting is one of the symptoms of consuming an acute dose of copper oxides - https://en.wikipedia.org/wiki/Copper_toxicity

I guessing it may have been something else that might have made you sick. 

 

Copper bowls are a mainstay in whipping egg whites

The Science Behind Whipping Egg Whites in Copper Bowls

 

Copper bowls is also used for the preparation of caramelized sugar and honey in making candy.

 

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the problem those of us who learn on our own is that none of these considerations are emphasized in the usual ways we learn.   maybe someone with the proper knowledge could write a simple explanation of why it is ok for mother earth to have deposits of chemicals and minerals that have been here for millenia but potters pouring some of those things onto the earth or into a river is wrong.

Depending on where these deposits are located they aren't necessarily leaching into the local water supply or various streams and rivers.  Often the nasty compounds are bound in ways that are less water soluble forms and as such are less harmful to various organisms in the environment, but after processing and refining by humans they become more concentrated, or are used in places where they have more potential to cause harm.  There are plenty of places where natural deposits of chemicals cause problems, such as areas that naturally have excess fluoride in the water.

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The copper bowls people use for egg whites and other culinary purposes tend to be clean of oxides.  Vomiting is one of the symptoms of consuming an acute dose of copper oxides - https://en.wikipedia.org/wiki/Copper_toxicity

I guessing it may have been something else that might have made you sick. 

 

Copper bowls are a mainstay in whipping egg whites

The Science Behind Whipping Egg Whites in Copper Bowls

 

Copper bowls is also used for the preparation of caramelized sugar and honey in making candy.

 

 

 

Yes, but you said...

 

  so I grabbed a copper bowl

 

...which is what I thought you were referring to.

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On the bubble issue. I fired a grid tile for a clear that I am thinking about using. I have a bunch of the grid tiles with bubbles at different amounts. I made two of the grids for test purposes. I only fired one first in my normal schedule. I am going to add a hold at 2095F for an hour, based on that other schedule that I posted a few days ago. I want to compare the differences of that hold with my regular firing to see if it makes a difference like the schedule on digital fire said it would. 

 

I will post results next weekend when I fill my kiln with test and run it. I am curious if it really makes a difference.

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Are you doing the hold on the way up? 

 

Yes. I will hold for one hour at 2095F on the way up. This is what insight said helps with the bubbles. We will see if it works or not. I have the extra grid, I might as well try it. It is for a clearish glaze. On my black clay, the clear is basically black, so that is what I want inside my my grey cups and mugs at the moment. So I want to fix the issue the best I can.. I will post the same tile without the hold and one with the hold and we can compare.

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