Firing cone 10 clay body to cone 8 with a 20 minute hold for drinking vessels

[ClayKatie]

I have been searching for answers for quite a while, finally decided to ask my own questions! I am learning the arts of ceramics at breakneck speed here, making alllll and the newbie mistakes in the name of knowledge acquisition! So I want to fire my cone 10 Laguna B Mix with Sand and Laguna Maya Red at cone 8 with a 20 minute hold. I am firing in oxidation in my 3 months old kiln with a cone 10 rating but I am so scared to wear out my kiln. I am making drinkware that has  a medallion and a lower portion exposed with raw clay. I want the clay to be appropriately vitrified, especially since i have exposed portions. I would be going with cone 6 clay except my access to clays is poor in my town. One art store in my area carrying all cone 10’s except one, a 90 minute drive to the nearest supplier and shipped clays costing twice as much due to shipping. I am starting to think it may be cheaper to buy the cone 10 if i can get away with a fairly long element life by firing to cone 8. Also, I love these two cone 10 clays so far, they feel do strong! I own an Olympic Medallion. Any experience with firing cone 10 in oxidation and/or firing down to cone 8 with cone 10 clay bodies much appreciated! Katie

[Min]

What do your witness cones show? Are you getting to cone 9 with that schedule?

Laguna's published absorption for the ^10 B Mix with sand is 1.2% and the Maya Red is 1% but these both come with a fudge factor of +/- 1%.  I'ld suggest doing your own absorption tests and seeing what your actual absorption is. Link to how to do that here if you need it, about 1/2 way down. Do the proper test with weighing and soaking a sample or two. Since staining of the unglazed clay could be an issue I'ld aim for 1% or lower absorption which I'm guessing you will be over.

I can understand your concern about firing to cone 10, maybe time for a road trip?

Welcome to the forum.

[neilestrick]

Whatever money you save in buying the cone 10 clay will likely be more than  wiped out by shorter element and kiln life. Take a road trip or pay the shipping charges for a good cone 6 body. Or see if the local shop can get you some cone 6 clay with their next order.

[Mark C.]

You either do the absorption test to see what your clay is doing (on the test bars)-but knowing that you are shortening the element life. I as Neil said just drive the 3 hours and get the right clay

Using cone 10 clay at cone 8 is not a good idea . The absorbtion test will tell the whole story-except the shortened life of elements

 

One note in ceramics a 10,000 things can go wrong (and you will find some do no matter what)and you are starting out with a few of them right off the bat. This can be issues with glaze and body issues righ tout of the gate. Take the drive and start right. The savings is not worth it my mind.

[ClayKatie]

Min, thanks so much, great advice! I will read up more on absorption tests. I like this practical way to visualize what the clay is absorbing at cone 8, 9 or 10. I may try just comparing some ink absorption on a fully fired cone 6 clay next to my cone 8+20 min soaked ^10, just to see... 

[ClayKatie]

Neilestrick and Mark C.,

I suppose it is probably wishful thinking on my part that my ^10 clay would be ok at ^8:).  But I have read that mid fire and high fire clays are much less absorbent than a fully fired low fire clay, even when they are not fully fired. Also i have read that for these high fire clays ^10 is the max firing temp it can take, but in many applications firing lower is fine. Probably not for drinkware though, i get it. My brain gets to bargaining with itself, 

[Callie Beller Diesel]

Your best bet really is to do an absorption test and find out exactly what that looks like under the firing conditions you want to use. We can tell you all day, but you wouldn’t be the first one of us that need to hold a thing in our hands to truly understand a lesson. 

[Min]

21 minutes ago, ClayKatie said:

Also i have read that for these high fire clays ^10 is the max firing temp it can take, but in many applications firing lower is fine.

If you are making functional ware from either a mid or high fire clay then the clay shouldn't leak even when there is no glaze on the pot. Absorption of under 1.5% is ideal. 

Clay is at it's strongest when fired to maturity.

[ClayKatie]

Well seeing as I had already built about 35 pieces out of this nebulous clay, (which I swore was a ^6 as I looked it up in Laguna’s online catalogue while I was standing over it at the art shop-need to upgrade my glasses again apparently) I begin my experiment and set my kiln. My pieces have thin walls, quite a bit of exposed clay and I am doing a slow glaze, I hope all these things add up to less heat work needed and more heatwork occurring at ^8. I also added in a 20 minute hold. My last pieces, done in ^6 clay to ^6 had a bit of a burnt look on some raw clay edges. Maybe my new kiln fires a little to hot? Again, arent I so good at bargaining with myself? Later I plan to go buy some ^6 B mix at the art store, this is too stressful!! 

[Mark C.]

You have to do the absorbsion test to anything about the end results. Underfired leaking clay is good for nobody no matter what the cost.

[ClayKatie]

Yes, nobody likes a leaky, moldy artistic coffee mug:) Yuck.

[oldlady]

katie, please do not feel bad.   this is really a good group of very caring people who want to help.  i have been where you are now and nobody offered any help.  that was a long time ago when the only education i could get was in books.   after all these years, i have learned a few things about working with clay and making things i can sell.   it sounds as though you have a reason to make this specific item.   has someone agreed to pay you for the mugs and you think you can earn that if you just find a way to fire the ones you have already made?

you are not being criticized, each of these answers are to help you learn that you really need to follow some "rules" to progress.   lately, there have been some questions that were not asking for an answer, they seemed more like challenges from some people who wanted to do stuff their way no matter what anybody suggested.   i read the answers here and realize that all the answers are past what you have learned.   you are still working on the alphabet and the answers are like reading shakespeare. 

it will take a lot of time and many, many mistakes before you will be able to do exactly what you want almost every time you touch clay.  try to find a way to learn the basics and not become unhappy when you run into the inevitable rock when you escape from the hard place. 

 

[ClayKatie]

23 hours ago, oldlady said:

katie, please do not feel bad.   this is really a good group of very caring people who want to help.  i have been where you are now and nobody offered any help.  that was a long time ago when the only education i could get was in books.   after all these years, i have learned a few things about working with clay and making things i can sell.   it sounds as though you have a reason to make this specific item.   has someone agreed to pay you for the mugs and you think you can earn that if you just find a way to fire the ones you have already made?

you are not being criticized, each of these answers are to help you learn that you really need to follow some "rules" to progress.   lately, there have been some questions that were not asking for an answer, they seemed more like challenges from some people who wanted to do stuff their way no matter what anybody suggested.   i read the answers here and realize that all the answers are past what you have learned.   you are still working on the alphabet and the answers are like reading shakespeare. 

it will take a lot of time and many, many mistakes before you will be able to do exactly what you want almost every time you touch clay.  try to find a way to learn the basics and not become unhappy when you run into the inevitable rock when you escape from the hard place. 

 

Thanks for this kind hearted comment. I do want you to know though that I definitely don’t feel bad for not knowing everything. And learning this craft, especially the challenges, does not make me unhappy. Do not worry for me, I delight in “learning the abc’s” knowing I am swimming around in a craft that is as old as human history. I realize there is more to know about ceramics than I can wrap my head around all at once and that does not embarrass me or make me think I should give up. The truth is, I have had many questions along the way and books and google and YouTube have been amazing but, well, they miss the mark after a while:). I am not one who needs to know it all to be happy(I do like to eventually kniw enough to control my outcomes!)I have other areas of my life where I am the  “expert”. Being the expert doesn't make me happy, learning and improving and the creative process, that is what makes me happy. I have learned a lot in a short amount of time and, frankly, it is awesome. I am loving it! And my pots came out pretty decent actually! I haven't had much time today for testing but I did soak a newly fired cup and a fully vitrified cone 6 body cup of the same design and then microwaved them both. I could feel no temperature difference. Now I’m sure someone will tell me how wrong or inaccurate that is, you are probably right, I’m still learning! Give people a break, its not a crime to learn something new, make mistakes and question “but WHY do you have to do it that way?”

[Hulk]

If you have a reasonably sensitive scale, try weighing before and after soaking with water - thoroughly dry off alla surface before second weigh.

My somewhat inexpensive US Balance unit reads to tenth of a gram (~$25 for the 2000 g unit).

[oldlady]

glad to hear from you.    the sources of info have increased greatly in the last 50 years.    the problem with some of that info is that without a solid background it is easy to think that all of it is of value.   then the problem becomes, "who should i believe?"    you will get good info on this forum, everyone has a specialty and you will get to know a lot if you ask questions.   

personally, i want to scream at some of the googled "experts" who give bad advice.   once the stuff hits the internet, it cannot be removed and thousands of people think they learned something good when they did not.

just over the past few months it seems that everyone with a kiln has to do something special with it's programming.   why do people slow cool with every firing?   and assume that if there is a thing called "slow cooling"  that the other, normal cooling must be called "fast cooling"  so it must be bad .   does anyone just use the manufacturers normal programs anymore?   maybe i am just getting old. and impatient  oops, much more impatient than ever.

[Bear Ceramics]

My kiln is a manual Fire Chief with a Dawson Kiln Sitter.  I have cone 10 clay that I had fired to bisque at the local clay supplier and wanted to finish in the Fire Chief kiln I just purchased used.

It will only achieve cone 8. Will this be satisfactory ??

[Min]

1 hour ago, Bear Ceramics said:

It will only achieve cone 8. Will this be satisfactory ??

Depends what you are making. Garden pots and decorative pieces or things like fruit bowls it would probably be fine if they don't need to hold liquids. For functional ware like mugs it probably won't be mature enough to bring the absorption down to an acceptable level and getting the clay to the maturity cone will result in a stronger pot. 

Main problem is if your kiln is rated as a cone 8 kiln and it will struggle to reach cone 8 after a few firings on new elements. You can sneak up on cone 8 by firing to cone 6-7 then doing a long soak to get to 8 but that is going to put a lot of wear on the elements. Could give it a try and measure the absorption of the clay at cone 8, for functional pots aim for around 1 1/2 % maximum. Which clay are you using? If at cone 10 the posted absorption is higher than that then if it was me I probably wouldn't bother glaze firing them (if they are for liquid containing functional pots). What cone are your glazes rated for?