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Pugaboo

Question... Why Bisque Fire To Cone 05 Rather Than Cone 04?

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The old pottery director bisque fired to cone 05 rather than 04... he never explained why. Is there a reason it would be done? I bisque fire my own work to cone 04 so am wondering if there is a benefit to one or the other.

 

T

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6 of one; half dozen of the other. Comes down to personal preference. Many community studios use 05 as it the bisque is hard enough to prevent over-absorption of glazes by beginning students who all count to 1003 (or 1005) at different paces. Not sure you'd notice a difference unless some glazes are real sensitive to thickness.

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Guest JBaymore

Slightly higher bisques help to assure that any sulfur and carbonaceous compounds are burned out of the clay body.  If you clay does not have "issues" in this department, other than glaze absorbtion preferences .... no real reason to go to 04.  MAYBE a tad more "durable" handling-wise........ but I'd guess the practical strength difference between 09, 06, and 04 is negligible.

 

Technically..... if the way you glaze/decorate your work does not need the advantages that bisquing offers in application...... bisquing is a waste of heat energy and labor time.  But few people want to take the time to learn how to effectively green glaze raw wares anymore (at the same loss rate as glazing bisque wares), and contemporary decoration processes pretty much require bisque pieces to do what most of us do..

 

I once fire some work in the wood kiln.

 

best,

 

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

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Ok hmmm since I'll be bisque firing student and amateur potter pieces mostly I would think a cone 04 would have its advantages. It would absorb less glaze, be a little more durable to handle, we also use Highwater Clays Speckled Brownstone as well a Little Loafers and occasionally Lizella, so the brown could use a higher fire and I know from my own experience LL has no issue with an 04 bisque, I'm not familiar with Lizella needs at all except firing one sculpture and it seemed very fragile even after bisque firing. I do know they have had issues with pinholes in the past so a higher bisque might help with that. This issue could of course be the glazes instead but I am working to remedy that as well by sieving and correcting the SG on the glazes.

 

It's not a cone offset, I know this for a fact he didn't know anything about those since I asked him on the glaze kiln why he fired to cone 5 rather than 6 and he said because it fired too hot so I asked why not just do a cone offset on a cone 6 and he had no idea what I was talking about. He also never used witness cones to actually test and see exactly how hot or cold either kiln is firing. I plan to run some tests when I fire next so I know how hot they are really firing as well as if I have any hot or cold spots. I've also started using kiln logs for both kilns so I can track how they are firing and know when I have issues approaching.

 

Attempting single firing with student work would be a disaster. Keeping them from slathering on their glazes is hard enough without adding that to the mix.

 

Thank you for helping work this through in my head. I think I will go to a cone 04 bisque from now on.

 

T

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Libels is basically a low fire clay: that has higher levels of nasties. Dicey at best in cone 6. Lizella runs around 5% iron: try red art instead.

 

Do a forum search for: " firing clay by color" under this section. It will give you some firing insights.

 

Instead of trying to learn clay chemistry- let me give a simple, easy way to judge clay purity. By which I mean, how much sulfur, organics, and carbons are in any given clay. It is these contaminants that create clay issues like pin- holing, bloating, and other fun stuff.

 

All you need to look at is the ( loi ) loss on ignition.

 

Clean clays run around 5% or less.

Semi clean around 10%.

Dark,high carbon, high sulfur run 15% an up.

The more nasties in the clay, the higher this number will climb.

If any one clay has over 10%, a slightly higher bisq should be observed.

Under 10%, lower will work just fine.

 

Nerd

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terry,  if it is just the color that people want, try robin teas' 2 ingredient clay.  50% redart, 50% XX saggar.  it is very strong and fires to a smooth dark red at cone 6.  this is the one that fell off the wall, hit the concrete floor, bounced and dug a hole in the drywall 3 inches up the wall and is just fine, no problems with the piece.   and it is super cheap to make.  have a "let's make some clay day" with all of the students.

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So I would say depending on what your doing or what setting you are in, you can adjust your bisque how ever you want.  Maybe even abandon it all together! I find it is the worst part of the entire process of ceramics, and is a huge bottle neck in my work since I only have one kiln. When I first started clay I looked into bisque temps, and there is a lot of different opinions. The best article I read was by some author who said he bisque his porcelain to 016 or something. Basically he said he just wanted it firm enough to handle being dipped and since he was only one working with this bisque ware he was able to understand the application process of having his clay that absorbent and not worry about students over glazing pots and such. 

 

I quit bisqueing my porcelain a few months ago. I haven't experienced any downsides to changing to this process. I spray my glazes though so if you dip it could be more troublesome. Although I have dipped plenty of small cups that were bone dry and everything seemed absolutely fine.

 

I am currently testing single firing Red Rock from High Water. I am having plenty of positive results without bisque so far. Although some might pop up as I continue exploring it. 

 

Making pots, loading bisque, firing it, waiting, unloading it, wiping it off, glazing it, firing it, unloading it.. I much more prefer the easy 5 step method: make, glaze, load, fire, unload. 

 

If I was you, and your wanting to be more efficient, you could start dropping your bisque down a cone each bisque until you think you find the sweet spot.

 

So fire 05 then 06 then 07 then 08 and keep going until you find the process is starting to cause problems. I did this in the oppposite manner when I was working with a really crappy body. I kept raising my bisque. I eventually got up to 02. Glazing was a pain.

 

Let us know what you end up doing.

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Guest JBaymore

All you need to look at is the ( loi ) loss on ignition.

 

Nailed it!   :)   (I'm not surprised.)

 

best,

 

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

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Guest JBaymore

So I would say depending on what your doing or what setting you are in, you can adjust your bisque how ever you want.  

 

One of the things I stress pretty heavily in my kiln firing course at the college and when I do kiln workshops is that "there is no such thing as a one-size-fits-all firing cycle."   Too many people (students in particular) seem to think that whatever firing cycles (bisque and glaze) that they have experienced wherever they are learning is THE firing cycle. 

 

Firing cycles are all about what is IN the kiln, how you work, and how you want it to turn out.  Understanding YOUR clay body(s) and YOUR glazes and what is happening in/with them helps you develop an appropriate cycle with YOUR particular kiln.

 

There are certain "general" things that act as guideposts....... but "the devil is in the details".

 

best,

 

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

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I could not agree more with John and Joseph ... once you have your own kiln, try other temps.

 

Group pottery centers require specific firing temperature RULES in order to guard the sanity of the loaders. If they give an inch they will soon have forty people absolutely needing their own specific firing profiles. Amazing co-incidence is these people seldom volunteer to load and unload kilns ... if they did, they would quickly be setting their own rules.

 

So ... when you finally get your own kiln ... experiment. Try different temps and firing profiles. Play a little.

The Cone chart has more than four numbers and which you use all depends on what you want to do next.

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Libels is basically a low fire clay: that has higher levels of nasties. Dicey at best in cone 6. Lizella runs around 5% iron: try red art instead.

 

Do a forum search for: " firing clay by color" under this section. It will give you some firing insights.

 

Instead of trying to learn clay chemistry- let me give a simple, easy way to judge clay purity. By which I mean, how much sulfur, organics, and carbons are in any given clay. It is these contaminants that create clay issues like pin- holing, bloating, and other fun stuff.

 

All you need to look at is the ( loi ) loss on ignition.

 

Clean clays run around 5% or less.

Semi clean around 10%.

Dark,high carbon, high sulfur run 15% an up.

The more nasties in the clay, the higher this number will climb.

If any one clay has over 10%, a slightly higher bisq should be observed.

Under 10%, lower will work just fine.

 

Nerd

Nerd, I just have to ask....where can a person find the LOI information?? 

 

Roberta

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Ok hmmm since I'll be bisque firing student and amateur potter pieces mostly I would think a cone 04 would have its advantages.

T

Please excuse this.....but I just can't help myself...

 

1. Pugaboo why do you want to bisque fire students to cone 04?

 

2. Nerd and John, I would say that students would have serious issue with LOI. After my dad was fired he could fit in a small urn. Now that is true LOI......

 

 

Jed

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JR - I am thinking 04 would be a little sturdier for them to handle, would absorb slightly less glaze, there is often a mixture of brown clay, white clay, thick pieces as well as thin in a bisque load. 04 seems a good compromise with all that going on. I am taking into account some of the issues I've been told they are having, pinholes, bisque parts breaking off easily when handled, heavy glaze applications causing running glaze when fired etc. I'm looking for a middle of the road solution for the art center.

 

I personally fire my own bisque to 04 with a hold BUT I tumble stack my load and it's packed ala Mark C with not an inch to spare, stuff inside of stuff, etc. I use witness cones in my own studio to make sure I am getting the correct heatwork and know the slow bisque to cone 04 with a hold gets me a perfect bend. I also do A LOT of design work on my pieces and want all that set nice on the clay so I don't have smudging or glaze interaction issues when I glaze. My glazes are mixed to an SG that I know gets me the correct amount of glaze on the pieces as well. I KNOW my own kiln and glazes but the Art Center is a different animal and one I am trying to tame.

 

T

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Roberta:

 

Raw clay will give loi values: not seen it on premix. The general rule of thumb is: the darker the body gets: the more nasties there are.

 

Been working on compiling all of this data for my clay book. Sadly some mills do not have their products tested. On premix: any body that is dark brown, reddish brown, or dark grey is automatically suspect. The farther the color moves from buff, tan to darker color: the more iron, sulfides, and organics there are. Secondly: darker colors also tend to have higher naturally occurring feldspar: usually potassium. This in turn also means the incident of large particles of potash are higher: which is the primary cause of pin holes, and if large enough: craters. Lizella is a primary example of a dark red clay with nearly 5% natural potassium: which can be larger particle in size.

 

Dark bodies are the ones that need higher bisq temps to burn off sulfur by products. These are also the bodies that should use a different glaze fire program: your schedule up to 2050f, then 130f to 2190 with a long hold, or 2230f with a short hold. Large particle potash in the clay takes an extended period above 2050 to burn off.

 

Nerd

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Libels is basically a low fire clay: that has higher levels of nasties. Dicey at best in cone 6. Lizella runs around 5% iron: try red art instead.

 

 

 

Nerd

Nerd, what have been your negative experiences with Lizella? I have not noticed any problems with cone 6 electric, soda, or salt. 

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Hi Douglas ..do not think we have met before.

 

I mix my own clay/ s, so my perspectives are usually very different than most. The two times in the past, I have try blending some recipes: I had some rather large pinholes for one. Did not have my microscope back then; but experience tells me some larger feldspar particles were present. Secondly, requires a bit more plasticizers than I care to use.

I have never fired it straight up, without blending other clays. Looking at the specs, I " assumed" it would not tolerate the heat. I would be more than happy to change my mind about it. Like so many mined/ mined products: probably got a bag with oddball debris in it.

 

Nerd

 

Side note: tired of auto- correct.

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Technically..... if the way you glaze/decorate your work does not need the advantages that bisquing offers in application...... bisquing is a waste of heat energy and labor time.  But few people want to take the time to learn how to effectively green glaze raw wares anymore (at the same loss rate as glazing bisque wares), and contemporary decoration processes pretty much require bisque pieces to do what most of us do..

 

I once fire some work in the wood kiln.

 

 

As a test, can I add a glazed bone dry piece into a kiln along with glazed bisque pieces in a glaze firing? 

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Technically..... if the way you glaze/decorate your work does not need the advantages that bisquing offers in application...... bisquing is a waste of heat energy and labor time.  But few people want to take the time to learn how to effectively green glaze raw wares anymore (at the same loss rate as glazing bisque wares), and contemporary decoration processes pretty much require bisque pieces to do what most of us do..

 

I once fire some work in the wood kiln.

 

 

As a test, can I add a glazed bone dry piece into a kiln along with glazed bisque pieces in a glaze firing? 

 

 

I know you asked John this, but yes you can. Just make sure that the piece you are adding is completely dry. Add a small preheat to the beginning of your schedule depending on how uncertain you are. If you are really certain do like a 1 hour preheat, if your pretty uncertain and you just want to be confident it is dry before it gets too hot, do a 2-3 hour preheat.

 

Let us know how it goes.

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When I used to bisque to 05, the porcelain was too porous, anything I dipped would get saturated and little air blowouts would happen all over the piece. Had to sand them down after glazing/before firing to smooth out the holes. Bisque firing to 04 took care of that, as well as some of the issues I was having with a red clay. Since I'm making mostly jewelry I dip the entire piece at once; there's heavy saturation, 06 sopped up too much glaze which caused the air blowouts.

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Other end of this, I don't fire bisque with cones. When doing pottery in the classroom, I used the mini cones and then the bars to 06. Back then I would stick around and watch the shut off of the kiln to that red orange orange color in the kiln.  When at home, with no setter, I used a few individual cones around the kiln to check through peep and other wise after firing. Found it really didn't matter once when one of the peep cones fell over, and I could not see it or any others. Fired the kiln to color and all was good with other cones. So years later, no cones, firing to color, but now closer to orange than before as pin holing was an issue. Yes it is only approximate, but if you get to the point where you are consistent in your memory of the color. . . . why not?

 

 

best,

Pres

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As a test, can I add a glazed bone dry piece into a kiln along with glazed bisque pieces in a glaze firing? 

 

I know you asked John this, but yes you can. Just make sure that the piece you are adding is completely dry. Add a small preheat to the beginning of your schedule depending on how uncertain you are. If you are really certain do like a 1 hour preheat, if your pretty uncertain and you just want to be confident it is dry before it gets too hot, do a 2-3 hour preheat.

 

Let us know how it goes.

 

 

Thanks Joseph

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Hi Douglas ..do not think we have met before.

 

I mix my own clay/ s, so my perspectives are usually very different than most. The two times in the past, I have try blending some recipes: I had some rather large pinholes for one. Did not have my microscope back then; but experience tells me some larger feldspar particles were present. Secondly, requires a bit more plasticizers than I care to use.

I have never fired it straight up, without blending other clays. Looking at the specs, I " assumed" it would not tolerate the heat. I would be more than happy to change my mind about it. Like so many mined/ mined products: probably got a bag with oddball debris in it.

 

Nerd

 

Side note: tired of auto- correct.

 

It definitely has a very groggy feel to it. I don't think it is grog since they don't do much processing to the clay. Very large particles and some students don't like to use it since it is very rough on the hands. I have only used it straight out of the bag, or wedged with Coleman's porcelain. At least with our studio glazes it seems to be good. It does seep slowly so sometimes adding porcelain slip to the inside of mugs and bowls can help prevent that.

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I have fired at cone 05 once (I am a newbie) but found in my Paragon kiln notes from my deceased friend who fired all of my sculpture that he bisque fired at cone 6 (assuming that should be cone 06).  Is there a benefit to firing at cone 06 rather than cone 05?  Needless to say I am terrified because I am a week and one-half from what will probably be my last show (72 years old) and can’t afford to lose any pieces!

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