Cone 10 Cone 6 And Cone 06 Clay Use Locally

[Mark C.]

After a comment on this forum.I did an informal survey of our area's clay usage. Meaning what types of clay is bought and used the most.My studio assistant works at the local clay supplier so its a pretty reliable survey.

Since I only know  about 2 other Pros using cone 6 clay of all my professional friends in clay (Mea on this board is one) the rest of us old timers fire in the high fire world.I see a few low fire and cone 6 folks at shows buts a small number.

I thought I would see whats going on clay wise locally.

The Junior Collage locally has a  large high fire (cone 10) program which include wood firing and gas kilns and does  minor o6 electric stuff

The Local State University does high fire cone 10 mostly and has low fire 06 work as well. You can fire your own cone 6 load if you are trained .

The local fire Arts center a private (adult and kids programs) ceramic place does mostly cone 10 gas firing some raku and you can pay to have a load fired to cone 6 if you provide everything.

Two High schools have cone 10 gas programs one also has a cone 6 electric going  alongside the cone 10(yikes) and another only has a cone 6 program.Most high schools have no ceramic programs

Secondary schools around here if they have ceramics its all con 06.

The clay supply store sells high fire clay the most by a long shot, second most popular is low fire  (06mostly to schools ) last is cone 6-mostly to hobbyists 

Thats our local clay story

 

[glazenerd]

Mark:

In researching modern clay formulation; most can be traced back to the early "studio potter" revolution that began after WW2. Up to that point, large ceramic houses controlled Europe and North America. Then Leach, Sanders, and a few others began the studio potter movement: which also meant they had to learn how to mix their own clays. Clay manufacturing did not start until after Vietnam, and did not gain much traction until the early 80's. The very first recipe was the old porcelain: 50/25/25 blend: 50% kaolin, 25% silica, and 25% feldspar. This recipe came about because the only kiln firing available was cone 10: there were no controllers like today. This recipe however was hard to throw because it had very little plasticity. Not long after, the 25/25/25/25 recipe was born: 25% kaolin, 25% ball clay, 25% silica, and 25% feldspar: which is called 50/50 porcelain today.

 

It was during the energy crisis in recent decades that cone 6 became popular. Instead of formulating clay for that specific cone: they just took cone 10 recipes and added more feldspars to them. Many clay websites tout their cone 6 clays as being the same as their famous cone 10 recipes that have been adjusted for cone 6. In the last two decades, particle size distribution (PSD) has become the dominant theory in clay formulation. While it focuses heavily on density packing, the accompanying flux molarity and other parameters have been pretty much left to chance. Locally, according to our supplier cone six clay is the most popular.

 

Now because of consumer demand, clay making is governed by economic demand. Potters do not want to pay over0.50¢ a pound for clay. So that forces the maker to use cheaper raw clays, silica, and feldspar. Wedging, coning, and other accepted clay practices came about only to remedy the problems modern formulation techniques have caused. Potters have come to accept problems with clay as normal, which they are not. Sodium for example causes a host of problems with clay, that would take me pages to illustrate and explain.

 

A true cone six body that has been specifically formulated for that firing range can and is every bit as vitreous and dense as cone ten. The problem has been that kiln technology, glaze technology, and equipment has progressed with modern times. Clay formulation has remained virtually unchanged since its inception in the 60's. There are no formula limits, no blending guidelines, nor any precise formulation rules that govern firing ranges. Even now I commonly see suggestions of using 200 mesh silica in a cone six body: which does not work very well. Until clay "limits" become the science like glaze "limits": there will always be problems with clay. There are such a broad range of high quality raw materials available, the problem is the pottery industry is not aware they exist. We just keep blending commonly known and sold clays in different ratios, and somehow expect different results.

 

Nerd

[GEP]

In my area (the DC/Baltimore area) the proportions are different. High fire fuel kilns are only at universities and art centers. Very few individuals have them. The only ones I know (or know of) are well off hobbyists (I don't mean "hobbyist" in a negative sense, anyone who has the space and funds to do this has earned it). Wood firing is immensely popular around here, done at art centers that offer community firings, but purely as recreation for most who do it. Those who make wood fired pots for sale are full-time employed and doing pottery as a sideline (nothing wrong with that either). Most of the full-time professionals are firing electric, to various temps from low-fire to cone 8.

[Pres]

In this area also there is very little in the way of ^10. Penn State University has an BFA/MFA program that has extensive kilns both electric and gas, along with soda/salt firing kilns. Advanced classed do kiln building. There was an Anagama, built by Jack Troy in Huntingtion, Juniata College but it was torn down in 2013, and Jack has two Anagama's I believe. Peters Valley also has a wood burner I believe. I don/t know as any local Grade schools have anything but electric, most of them ^06, the HS I taught at was the only one using ^6, but now the JrH does also. . . . an old student of mine teaches the classes.

 

 

best,

Pres

[Marcia Selsor]

I dropped to ^6 at the university program where I taught back in 1980 after the energy crisis. My clay body was one formulated by Chip Clausen at the Bray clay business. My reduction ^6 glazes have been published including those in Micael Bailey's Oriental Glazes.They are the only ^6 glazes in that book. Many community programs have dropped their firing temps to ^6 including Archie Bray classes and The Clay Studio in Philadelphia. If the clay is vitrified and the glazes look good, so good that they can't be distinguished from ^10, then why spend 50% more on energy? because that is the consumption from ^6 to ^10..according to pyrotechnic charts I have studied. 

Even at the Red Lodge Clay center , there are people firing at all ranges. Many using ^6. Maybe Northern California potters are clinging to their traditional temps. Its hard to change if you are professionally developed after decades of refining.  Good surgery Mark, but I don't think it is nationally the case.

 

Marcia

[neilestrick]

I think colleges and universities are doing a disservice to their students by focusing their training on cone 10 reduction. 99.9% of those students will not be able to own a gas kiln when they get out of school due to zoning restrictions. A friend of mine that runs the ceramics program at a university on Colorado switched his program to cone 6 oxidation for that very reason. Cone 10 reduction is great, and I did it for many years, but it's just not practical or affordable for most people any more. It costs a friend of mine 4-5 times as much to fire his gas kiln to cone 10 on propane as it does for me to fire the same amount of pots with electricity to cone 6.

[glazenerd]

I think the future of pottery will change yet again. Cone 2/3 and cone 04 porcelain ( and colored) will become a major portion of the market over the next decade. Properly formulated 04 frit ware is vitreous and functional; even though it achieves that from the high glassy matrix of frit. Cone 2/3 will be a little slower to catch on, and will be more dependent on glaze availability for that range. As Marcia pointed out, cone 6 requires about half the power of cone 10 electric: cone 2/3 would drop that another 25-30%. Then the issue of element longevity comes into play.

 

The discovery of Meissen porcelain changed pottery in Europe in the late 1700,s. Then in the late 1800's, tactile Doat, Maria Longworth Storer, and a host of others changed pottery yet again. Then in the 50-60's, the studio pottery movement bought us to where we are today. Rather potters realize it or not: our industry is going through another period of historic changes. Personally, I would like to be part of those changes, and help to shape the definitions of pottery for generations to come.

 

Tom

[oldlady]

well, tom, your fabulous porcelain is well on the way to do just that.  wait until the world gets its fingers into it.

[Dick White]

Interesting thought there. That would bring the intersection of studio pottery "craft" (functional high-fire) and ceramic "art" (colorful sculptural low-fire) closer to a common firing point. If the clay body producers would get on this wagon so that there is a reasonable availability, the glaze world will quickly follow. I would think that the path here will be similar to the transition from ^10 to ^6 - a few well-regarded luminaries doing it, showing both what can be done and that it is legitimate for a serious potter/artist.

 

I understand the points made by some previously in the thread that gas kilns are typically in the province of the higher academic institutions and not accessible to those working in small studios, esp. at home. But one of the things we tell ourselves is an attraction of the program at our community college is that it is an opportunity to do interesting things that you can't do elsewhere. And, just my opinion for now, could change at any moment, I think if there were more people with sufficient training and experience as students firing gas kilns, there would be a body of knowledge/personnel available to actually fire such beasts in community studio settings that won't consider it now because they don't have anyone who knows how to do it.

 

Taking this notion back to the lower firing clay body discussion, what is the experience (if any) with low-fire reduction? One of the theoretical advantages of reduction firing at ^6 and up is the added strength/vitrification of body reduction. Current low-fire bodies don't vitrify in the first place, so what's body reduction going to do there? But if new bodies are developed to vitrify at the lower temperatures - is reduction another side of the exploration?

[curt]

I very much doubt that the future of this medium will turn on firing costs.

 

And if it does I will hang my head in despair...

[neilestrick]

I think if there were more people with sufficient training and experience as students firing gas kilns, there would be a body of knowledge/personnel available to actually fire such beasts in community studio settings that won't consider it now because they don't have anyone who knows how to do it.

 

 

I don't fully agree that the problem is lack of experienced people to fire the kilns. There are a ton of other issues keeping people from having gas kilns in their studios:

 

1. Cost. Even if you build your own, by the time it's fully hooked up and vented you're going to spend at least $20,000. You can get a lot more kiln space for the same money with multiple smaller electric kilns.

2. A 22 cubic foot (stacking space) gas kiln has a much larger footprint than an equivalent size electric kiln.

3. Gas kilns are noisier and smellier, and can't be put in the corner of the studio like an electric can. They really need a dedicated kiln room. 

4. Gas kilns require much more tending than electrics. They just aren't nearly as convenient.

5. Building permits. It is increasingly difficult to get a permit for a gas kiln. I know this from experience. If you're in a freestanding building of your own, it's possible. If you're connected to other businesses, the fire codes get really strict and it's near impossible to deal with, and very expensive.

6. Batch size. If you're running a community studio, you need to be able to run small batches- kids classes, birthday parties, scout troops, summer workshops, etc. You can't wait to fill the gas kiln.

7. Glazes. Not everyone likes earth tones. At some point you need some bright colors, which cone 6 oxidation is really good at. It also gives your students the opportunity to supplement the class glazes with commercial glazes they purchase themselves.

8. Consistency. One of the biggest complaints from students in community studios is a lack of consistency in the firings. Multiple people firing the kilns generally means multiple results. Electric kilns don't have that problem.

[neilestrick]

I very much doubt that the future of this medium will turn on firing costs.

 

And if it does I will hang my head in despair...

 

Firing costs are a big deal. If I had to pay for propane to fire my kilns, I would have to charge at least twice as much for clay to cover the firing costs, which would definitely affect my business.

[Mark C.]

If costs are the factor keep in mind where we live electricity is a very high cost over double what it is in most areas.My gas car kiln fires cheaper than 3 electric loads (same volume)

Natural gas is cheap-(propane not so much)Natural gas is in lots of areas. All my professional friends on the west coast fire with natural gas

If I was in the midwest where electric is super cheap its would be a different story maybe.

[PSC]

Cone 6 dominates for the functional potter in my area. I would love to do cone 10 reduction...i fired my universities giant gas breathing giant and would love to have one at my disposal. I doubt i could install one in the yard legally and the center where i teach would not want to go to the expense of building or buying a gas kiln.

[glazenerd]

Dick:

One of the primary stumbling blocks to lowering cones was overcome a decade ago. Back in the 60's, an 120 mesh was considered fine. In the 90's, 200 mesh was common, and 325 was rare. Now 325 is the standard, and finer grades are readily available. In the U of I study back from the 1930's: it was reported that finer mesh materials lowered melting points considerably- this is now common knowledge.

A 325 mesh silica melts at 3150F, Imsil A25 melts at 2950F, solely based on its particle size. There are ball clays out there running 0.31 microns: which is close to the plasticizer particle size range. I have been talking to a mine that is starting to produce a 625 mesh potash feldspar,with 13.50% potassium. Nano- particle technology has and is emerging rapidly. Particle sizes has created the biggest hinderance in lower clay body cone temps: but that issue was resolved over a decade ago. The problem has been the clay industry has not incorporated that into modern chemistry.

If 325 mesh potassium starts melting at the 1750F range, then a 625 mesh would lower that by 100F. That puts the whole concept of cone 2/3 well within reach of practice and doable. The technology to lower cones, while maintaining functionality has been around for over a decade. The clay industry has chosen not to take advantage of it. Given that finer mesh is now common, economics is no longer a viable objection.

[Mark C.]

A few points here-I did not think this would raise this much dust here.

 

Tom great reading your historical piece-Felt you were speaking to the choir as I lived most of that since 1969-I will look up some of the old formulas from when I made clay for the university as a work study job in collage and post them.

One other thought is industrial materials drive the clay process on whats available at what times in the past .

 

 

In the 60's the Hobby thing was slip molded cone 06 (any CM from this days will support this). The easy thing was slip shops selling molded bisque wares . people bought electrics as they learned those processes. When I arrived here in Humboldt in 1971 there where what we referred to (sorry about this Oldlady-no harm intended) as Oldlady slip shops.Now there are none in this county-zero been that way for a few decades now-even the paint your own rebirth return craze is dead here now.

The natural transition for folks in terms of easy is an electric kiln-its just easier -all the way around-that the way I view it-The market is driven by this fact.

 

Now as Neil says its not fair for universitys to teach high fire I have to disagree strongly- very strongly and heres why-I feel that the schools need to teach it all-cone 10 cone 6 and cone 06. I learned all I could sponge up in my collage days from low fire to high fire -Throwing to mold making-you need to learn it all-they just did not do or teach cone 6 in the early 70;s.

All my teachers where fresh out of Alfreds University and cone 6 was not on that schools radar either at that time. More knowledge is better I feel Neil and if you pursue a BA in art with ceramics as your main theme than a full knowledge of all temps is far better than only some.

[Min]

Think Mark is referring to a post I made about choosing a gas or electric kiln on another thread and the amount of info plus glazes available for ^6 electric versus ^10 gas reduction. In my area the local University, does teach low, mid and high fire with electric and gas. I know that in the past few years there has been 1 or maybe 2 students who had the exclusive use of the gas kiln for ^10 work as none of the other students were interested in producing work from it as they won't be able to fire gas after graduating in most of the urban areas here. ^6 electric for the most part.

 

Tom, still concerns me with using 5 micron silica as the ImsilA25 is. 2500 mesh. How long does that stuff hang around in the air for? 

[Marcia Selsor]

Mark,

Your comment about the high rate of Electricity in your area explains why so many are still firing to ^10 with gas.

I think the fuel costs influence much of these decisions.

Marcia

[neilestrick]

Now as Neil says its not fair for universitys to teach high fire I have to disagree strongly- very strongly and heres why-I feel that the schools need to teach it all-cone 10 cone 6 and cone 06. I learned all I could sponge up in my collage days from low fire to high fire -Throwing to mold making-you need to learn it all-they just did not do or teach cone 6 in the early 70;s.

All my teachers where fresh out of Alfreds University and cone 6 was not on that schools radar either at that time. More knowledge is better I feel Neil and if you pursue a BA in art with ceramics as your main theme than a full knowledge of all temps is far better than only some.

 

I agree that they should teach everything, I never said otherwise. But in studios with gas kilns, the focus is cone 10 reduction, and that is where I think the problem lies. They should absolutely have gas kilns and electric kilns and raku kilns and wood kilns and soda kilns and salt kiln. But the focus should be on where the bulk of the students will be working once they get out of school. Isn't that the whole point- to give them the skills to be potters/ceramic artists when they graduate? Does the engineering college teach their students to use computer programs that aren't used in the real world? Does the computer programming department focus on DOS? Too many university clay programs don't teach to the reality of life after graduation.

[glazenerd]

Mark:

Potters are a passionate bunch; a requirement for our craft. I think your comment bought up a much needed and long overdue discussion.

 

Min: before I answer your question: " avoid breathing all silica dust, use appropriate respirator when working with dry glazes."

 

I do not use Imsil A25 in clay, but Imsil products that are 800 mesh. Imsil is an agglomerate product: it clumps like powdered sugar until it hits water. I can visibly see dust coming off other silicas, but none off Imsil. However, I do know there is dust rather I can see it or not. Ron Roy sent me a letter after reading my posts in the SAS thread about his testing of silica. In sieve testing a sample of 200 mesh, only 10% was retained on the screen: meaning 90% was finer. Testing 325 mesh, over half passed through the screen. Point being, any given bag of 325 mesh, is in reality 325 up to 600+ mesh. Modern milling is producing ultra fine meshes, and 325 is just a number these days. Your concern over silica dust is justified.

 

Nerd

[Mark C.]

Mark,

Your comment about the high rate of Electricity in your area explains why so many are still firing to ^10 with gas.

I think the fuel costs influence much of these decisions.

Marcia

I also think the rural nature of an area over an urban area is also a factor at least as time went by.Meaning back in the 70-'s around here you could assemble a pile of bricks and get a permit to get gas to it. Now thats just not the case-It could be in city and urban areas even in the 70's that was not the case. I know thats what propane users often skirt the permit thing with natural gas companies and use permits.

Electrics do not trigger permits unless the entire service needs an upgrade.

Electricity has always cost a fair piece in this state. Its practically free where Nerd lives-they may even pay him to use it-like back in the rural electric expansion of electric use in this country-they wanted people top use it and expand the network-it was very low cost-must have stayed that way in parts of the midwest.

[oldlady]

mark, i remember that the electric company in detroit gave away light bulbs free.  they also repaired my electric stove free.  a long time ago.

[Mark C.]

Tom said

(Now because of consumer demand, clay making is governed by economic demand. Potters do not want to pay over0.50¢ a pound for clay. So that forces the maker to use cheaper raw clays, silica, and feldspar.)

​This made me go out and look up my Dave's Porcelain and Babu Porcelain prices.

Keep in mind this is for way over 12 tons of clay-large quantities pricing.NOT including trucking which adds more cost.

The Daves in January  2017 was .21 cents and the Babu was .43 cents

I have since touring the plant in the 80's  in so-cal and switching over to it from a Westwood clay I had been using.(Westwood was the original clay company for you youngsters  out here on the west coast that got bought up by Laguna as they expanded into a monster sized company-they also bought up the midwest Ohio clay plant as well as the Florida one and Anxner )Laguna moved into Westwood facility which I used to go to in the late 60's and early 70's to get materials.

I have been very happy with this porcelain-it throws big or small and does not crack.Its cheap and works very well and is hard as brick when fired to cone 10 or more.I have learned all its secrets and the only downside is its not as white as Babu but it twice the cost.The public loves the glazes on it.

As to clay costs I never sweat that much-if clay where double than I raise my prices a tad to cover it.I had to look up my costs-cost usually is not a driving factor for me.What is way more important is it works for me-When you work with say 10 tons a year for many many decades it has to work well (the clay that is)I have only had this clay screw up once and of course its the maker that did this . Mistakes can and will always happen.

​I'm glad you are making a body that works as what I have seen is most cone 6 bodies do not work well-folks have issues with them-its well documented on this board.

[Pres]

I have done cone 10 red. and loved the surfaces, and the durability along with the Copper Reds, and other glazes. I decided on ^6 electric because where I lived, even though in a commercial zone, at the edge of small downtown, gas was not really an alternative. I purchased what I could afford in largest size at the time, and had decent turn around time, usually filling a load in a week, during the school year when getting ready for shows in the Spring. I was able to double that during the Summer time when I did 16 hr days trying to get ready for shows. I really don't know what I would do with a 30 cubic foot gas kiln anymore. I did check on a gas line from the front of house where it would have had to come in to the back garage. . . 1.5K. Nope don't worry about it, and propane is just not an option to me as a large enough tank would set practically on my house as there is very little yard around the house. NO option. In the end, I believe ^6 is viable, durable, newer glazes since I started out are much more pleasing in surface and color, so until I quit potting and get potted, I'll stay where I am.

 

 

best,

Pres

[glazenerd]

TY Mark:

 

The introduction of my book gives the history of modern clay formulation starting from the studio potter movement of the 50-60's. I have been reading books from the 60's on clay formulation, which sound and read like the books written in the last decade. In 1933, a short two paragraph article on SAS formulation was proposed and quickly dismissed by his peers. (I feel his pain). Although he did not give specifics, he simply suggested that the ceramic industry should explore the SAS theorem, which was being adopted by other industries of the time.

Modern clay formulation has two serious flaws, and in the last decade has added a third. It is just clay to us, but it is still chemistry regardless of how we use it. When you break basic chemistry laws, there will be problems rather it is clay, glaze, or rocket science. Hopefully there will be a lot of changes in clay formulation over the next decade: if I have anything to do with it, there will be.

 

Nerd