Cone 10 or Cone 6 reduction

[Antoinette Brown]

Hi I am an amateur and do fire cone 10 gas.  My kiln has two burners. I really think that it would be reasonable trying out cone 6 reduction firings because of the amount of gas needed. I looked up recipes in glazy and the results seem nice. What do you think? 

Are there constraints if I use cone 6? Aesthetics? Ash glazes and glazes with natural materials? 

I'm not a big fan of very colourful glazes.

[Mark C.]

I am a cone 10 lifetime potter. The cone 6 is a bit less in gas  true but fluxing issues and materials to do that also play into costs as they cost more. I personally feel its easier glaze wise to fire cone ten. The choice of clays is larger as well and the clay costs a tad less. But i'm not a cone 6 potter.

Many here are electric cone 6 potters and if its an electric kiln cone 6 makes more sense. 

[Antoinette Brown]

I do agree. If I read in forums everyone with cone 6 has some sort of problems and me having no clue what I'm doing have no problems other than a glaze recipe comes out different then what I expected.  However, I fired my new kiln (and there is no manual anymore  and the supplier is not around anymore I think it was built 30 odd years ago or more) and the gas consumption was simply nerve wrecking and the difference between 6 and ten more than significant. I know that the packing has huge implications. It was also completely weird that if I closed the flue at least two thirds and the kiln was clearly in reduction the temperature was rising and when I opened the flue and the air at the burner it was falling!

i still have some packets of cone 10 clay laying around and some buckets of reclaim so I'll see.  It also depends a bit what I find locally because I want to include local stuff because I like it and also the next clay supplier is two hours drive away. I'm in Australia and sometimes local clays are high fire, but that's altogether a different topic.

[Bill Kielb]

A damper opened too far let’s out too much heat and let’s in too much primary air - cooling the kiln. A damper closed just right keeps the maximum heat in and provides just the right amount of air (10:-1) for combustion for the fuel to burn most efficiently. A damper closed that begins to smother the flame and builds pressure in the kiln while a jet begins to emerge from the spyholes is in reduction and most kilns are marginally powered so their temperature rise stalls or even falls.

With proper gas pressure and coordinated damper operation you may be able to save a bunch of gas and some time as well. Folks usually find the best damper position and gas pressure combination throughout the firing (often every 30 minutes or so). Rarely does the damper position change by more than 1/4”-1/2” at a time once ideally found for each operating pressure.

[Antoinette Brown]

Thanks! This firing was the worst I've ever done. I don't blame it  on the kiln but I have to draw some pictures and ask about the load. In my old port- o kiln it was very crucial to load it in a certain way. And def. the lower shelf had to be 7 cm off the floor. The lady I bought it from didn't do high firing she did lovely sculptural work with a really nice red clay she dug in her yard. She told me that she left the flu open and the lower shelf wherever. 

I decided that I buy a couple of bags of cone 6 once I drive past that shop (which does not happen often) and simply give it a try and compare. 

I am not super methodical, but with the old kiln I figured it out, but yes I should do that more methodical and  match the pressure (I got nearly up to 30!!!)

 

[neilestrick]

The amount of gas used to get to cone 6 is roughly the same as the gas used to get from cone 6 to cone 10. So yes, you will use a lot less gas.

16 hours ago, Antoinette Brown said:

If I read in forums everyone with cone 6 has some sort of problems

I think there are two main reasons for this. First, there are far more people firing cone 6 than cone 10, so you're going to see more comments by them. Second, people come to forums for help finding solutions to problems. All the folks who aren't having problems are not posting about it on forums.

If you fire at cone 6, keep in mind that most all commercially available glazes are formulated to fire in oxidation. That doesn't mean that they won't do some amazing things in reduction, but you'll have to do some testing to see how they'll react. Cone 10 glazes can be lowered to cone 6 with the addition of some frit, often as little as 3-5%.

Brown clay bodies will take some testing, too. If it's a dark body in oxidation, it will probably not be suitable for reduction. Light brown bodies will go dark. White stoneware bodies may go gray, just like at cone 10.

https://ceramicartsnetwork.org/daily/article/Five-Reasons-to-Convert-Cone-10-Reduction-Glazes-to-Cone-6

Georgies cone 6 glazes in reduction

 

[neilestrick]

If you're using a white clay body, you'll find that many glazes are unaffected by reduction, or affected very little. With a brown clay body you're going to get more interaction between the body and the glaze, which will result in a different look even if the glaze itself isn't being affected by the reduction. Test, test, test.

I've got a couple of glazes that I used at cone 10 reduction for years and years, converted them to cone 6, and they are indistinguishable from the original when used on a white body or a speckled brown body when fired in oxidation.

[Kelly in AK]

I do cone 6 reduction soda firings. It works fine.

I don’t believe the firing range is any more prone to defects than cone 10. Mid range firing is developing rapidly, over decades rather than centuries.

 @neilestrick hit the nail on the head. It’s worthwhile to give it a try.  You’ll see fewer glazes on glazy designed just for c6 reduction, but they’re there. 

One big difference is c6 glazes are mostly fluxed with boron instead of feldspar, so that means you’ll need some frits in your workshop. I get by fine with just two: Ferro 3124 and 3134. Gerstley borate works too, I gravitate towards frit based glazes because they’re easier to fit without crazing. Strontium and wollastonite are a couple more flux ingredients that see more use at cone 6. Natural ash melts above cone 6, but there are fake ash recipes that appear to produce lovely rivulets just like the real thing.

Another note on the brown clays, like Neil said, they go darker in reduction (a buff colored clay in oxidation looks iron rich in reduction), but some real dark ones can also bloat and pinhole glaze pretty badly. 

[Mark C.]

Since you are down under you should see what the grit situtaion is from suppliers as well as cone 6 clays. Babs is a down under potter on this site as well so she will have a handle on some of this. Your materials are not same to some degree as ours. Frits may be the case as well. Check that out.

[Antoinette Brown]

thanks for the input all! I will try it out and compare simple. I'll start with some white glaze recipes  or other rather simple ones.  Regarding firing I know that with my old kiln the way I stack (or stuck??) was important.  I always did half shelves in a staircase or alternating. This kiln has two burners on the right and the flue on the left downdraft. I guess what I got wrong was that  the right shelf I only set it around  3 cm from the floor. I wonder which way is the right way to stack 1) shelves on the right and left at the same height with a gap in the middle 2) shelves on the left lower and the right higher  3) Shelves on the right higher and on the left lower. Also: big spacing on the bottom or on the top? 

[Kelly in AK]

A white glaze I’m using now is based on glazes from John Hesselberth. It may be one of his glazes, I can’t remember. I just know I like it and it works. 

EPK- 32

Ferro frit 3124- 31

Wollastonite- 23

Silica- 14

add:

Zircopax- 12

I snapped a couple pictures of it from a cone 6 soda fire. The speckles are from the clay body. It’s a dark iron rich body mixed half and half with a white stoneware. The dark clay bloated awfully by itself, mixed with the white clay I regularly use it turns out ok. The glaze is satin matt if slightly underfired.

As for stacking your kiln, I suggest you make a new post in “Equipment Use and Repair,” posting any and all pictures of the kiln will help people answer your questions. 

[Antoinette Brown]

That's a nice white! And it has all the characteristics of a cone 10 glaze. It's maybe these heavily coloured glazes which did put me off in the past. I do a lot of RIOX backwash on texture and then glaze over it. Good idea with the equipment, I am in the wrong category!

[neilestrick]

18 hours ago, Antoinette Brown said:

This kiln has two burners on the right and the flue on the left downdraft. I guess what I got wrong was that  the right shelf I only set it around  3 cm from the floor. I wonder which way is the right way to stack 1) shelves on the right and left at the same height with a gap in the middle 2) shelves on the left lower and the right higher  3) Shelves on the right higher and on the left lower. Also: big spacing on the bottom or on the top? 

Can you post some pics of the kiln?

[Callie Beller Diesel]

About 6 years ago I made the switch from cone 10 reduction to cone 6 oxidation, so I can share a few observations about that.

I also don’t think cone 6 has any more or less problems than cone 10, but they are a different set of considerations. I find I have to be much more aware of “bucket behaviour” for cone 6 glazes than I did with cone 10, for instance. But with cone 6, the turnaround time is faster, which is pretty satisfying. I don’t know if the same holds true in Australia, but I found that my clay got exponentially less expensive, but my glaze materials got more costly.  But I buy more clay than glaze stuff, so. 

It took a good year of testing to refine things to get to where I felt like I understood what was going on. Learning about the different changes that happen to ceramic materials at different points in the firing helped enormously, so I think you’re on the right track with focusing on learning how to fire your kiln properly. Understanding how heatwork affects glazes is pretty helpful.

Switching to cone 6 made me a better chemist and gave me a lot more understanding of my materials. I found that focusing on firing the clay body to proper maturity solved most of the glaze problems that I encountered at cone 6. Often the focus at cone 10 is only on the glaze.  If you’re making functional work, you should do a bit more due diligence around testing for porosity at cone 6. Sometimes what the manufacturer recommends on the box is not what you get out of your own kiln.

[Babs]

Need to run a meticulous logbook for every firing. Time ,hours on,psi reading, temp rise,  positionif  damper, air intakes.and importantly results of glazes used. Total length of firing. A photo of kiln stacking would be good too . Once you've found your cool spots you can place glazes which don't mind that there.

The sculptor may have been only fIring to a low cone.

Aftwr you get your bagwall in, don't think your focus needs to be as much on the stacking, but gas, air and damper positions