Cone 6 Oxidation Results Group 1
by Terry Rorison
Since I have made the decision to concentrate on firing at Cone 6 oxidation rather than Cone 10 reduction, I have begun glaze tests to build a palette of colors and finishes to choose when glazing pieces. I also have the desire to produce the variation in the glazes that is similar to the effects of reduction on the glazes while retaining the brightness that is possible in oxidation firing.
Thus far I have batched between 80100 different glazes, the formulas for which have been found from publicly available sources. After firing these tests in an electric kiln to Cone 6, I have photographed each and am making them available to potters with the accompanying formulas.
Since this is my second attempt to post this (having lost hours of work due to some glitch in Blogspot), I am breaking the postings down into smaller groups to minimize risk if a posting gets lost or deleted. I will make a more detail explanation of my methodology at a later time. All tiles were photographed with a Nikon D60 in a light tent with two outside lights and flash. Each photo was cropped but otherwise not altered by software.
As always, comments and input are desired and welcome. The results are posted in a random fashion and this first batch was fired in a programmable kiln with a two hour preheat at 200 degrees and a program that ramped up the temperature to Cone 6 with the kiln being shut off and cooled normally. I will produce a set later with a slower cool down rate to promote crystal grow.
Formulas are shown in decimal format with 0.1 being equivalent to 10%. Two clay bodies were used and glazes were fired on each. The fit and visual difference produced by the two different bodies was very slight. A white stoneware from Standard Ceramic #181 was used and a studio mixed stoneware body that is an adaptation of Val Cushing's Cone 10 Wheel Wiz. The stoneware has low iron and fires out to a buff color at Cone 6 oxidation.
Tip: Click on each photo to enlarge. Then click again to enlarge some more. There is a lot of detail to be seen.
Tip: Click on each photo to enlarge. Then click again to enlarge some more. There is a lot of detail to be seen.
2
2  Jen's Juicy Fruit Variation (Red Matte) C/6 Totals 100%  
EPK  8  
Gillespie borate  7.2  
Nepheline syenite  39.2  
Flint  9.6  
Whiting  8.8  
Lithium carbonate  7.2  
Standard Ceramic's Red Stain  8.0  
Soda ash  8.0  
Titanium dioxide  4.0 
4
 
5
6
8
 
12
 
17
 
18
 
21
 
36

39
Red Rust Bottle  # 147 Rusty Bronze cone 6 over all of it, with #55 Raspberry Red over top part to middle, #140 Hansen White over the neck to line at bottom of neck all cone 6 oxidation. Red shows as a nice blush on the surface. Glazes were applied by dipping with no special treatment.
39  Clear Base Blue C/6  
Feldspar G200  0.2  
Frit 3134  0.1  
Wollastonite  0.2  
Flint  0.185  
EPK  0.2  
Talc  0.115  
Cobalt Carbonate  0.01  
Copper Carbonate  0.0075  
Red Iron Oxide  0.03  
Rutile  0.06 
43
43  Kaki with Gillespie Borate C/6  
Gillespie Borate  0.27  
Flint  0.253  
Custer Spar  0.169  
Talc  0.118  
EPK  0.042  
Red Iron Oxide  0.128  
Bentonite  0.02 
Red Rust Bottle
Red Rust Bottle  # 147 Rusty Bronze cone 6 over all of it, with #55 Raspberry Red over top part to middle, #140 Hansen White over the neck to line at bottom of neck all cone 6 oxidation. Red shows as a nice blush on the surface. Glazes were applied by dipping with no special treatment.
This is a gold mine for anyone looking for cone 6 glazes! All the testing is done and you can try them out in your own kiln and know what to look for!!!
ReplyDeleteThanks, Karen. Testing still proceeds in that I am a batch of the same glaze tiles ready to be fired to Cone 6 with a controlled cooling to examine to effects on the glazes that contain rutile, titanium, zinc, and red iron. I will post those results next to the "normally fired" (up to Cone 6 and off) ones shown here.
ReplyDeleteTry a slower cooling rate in your electric/oxidation kiln. These are not quite what they should be. The tomato red is not there...the iron needs a slow cool in order to form a crystallized matrix...iron red. You can try stopping your fan/vent at the very end of the firing and close the kiln, the top spy hole if open to help with the fan. A tighter load and closer kiln shelves will help with the slow cool too. Good Luck.
ReplyDeleteDarrell, I agree with your comments. Have programmable kiln so slowing the cooling rate is on my agenda. I did one batch of test tiles with a programmed cooling from 1700 > 1400 F but there was something wrong with the thermocouple and the witness cone 7 was flat on the batch of cone 6 glazes, so I couldn't compare the two batches and I suspect some of the glazes were overfired but I don't know by how much because 7 was flat and I did not put any higher cones in that firing. Have since fixed thermocouple so I plan on doing more with controlled cooling.
ReplyDeleteAdded a picture of some of the glaze combinations on a bottle at the end of this article with the three glazes identified in the order of glazing. The glaze tests with formulas were broken up into 4 sections and the numbering is random. See November's archive for the Cone 6 oxidation trials and formulas.
ReplyDeleteit was beautiful. Thanks
DeleteThanks, Linda.
DeleteToo technical for me, T but like the red rust bottle!
ReplyDeleteLove the blog.
ReplyDeleteI am wanting to make few of these glazes and I have a couple questions.
1. Emily's Satin Matt #21 only has 91% clays etc. I didn't think the colorants eg zinc ox or copper carb counted.
2.#36 blue green is at 102% not counting colorants....Is this OK?
Thanks so much
Darci, This is what I batched for a 300 gram test. Could have adjusted all to add up to 100% but the ratios would still be the same. Terry
ReplyDelete21 Emily's Satin Matt C/6
300 gr
Kona F4 Spar 0.52 156
Whiting 0.19 57
EPK 0.14 42
Zinc Oxide 0.09 27
Flint 0.06 18
Copper Carb 0.06 18
Bentonite 0.01 3
Water  80% 257
1.07 321
36 Blue Green cone 6
300 gr
Gillespie Borate 0.22 66
Strontium Carbonate 0.04 12
Whiting 0.11 33
Custer Feldspar 0.38 114
Flint 0.25 75
Cobalt Carbonate 0.005 1.5
Chrome Oxide 0.01 3
Bentonite 0.02 6
Total 1.035 310.5
Water  80% 248.4
What is the firing schedule for the tests? I live in France and I don't fire to Cone so and so but up to 1260°C in oxydation ? Thank you Evelyne
ReplyDeleteThe firing cycle is listed on the Group 5 posting. I actually fire to 2197 F (which is about 1205 C and hold for 30 minutes and the cone 6 melts perfectly. See schedule: http://wpapotters.blogspot.com/2011/10/cone6oxidationresultsgroup5.html
ReplyDeleteYou are brilliant! Thanks so much for doing all this work for all of us. When I started potting 40 years ago, my training had been all in cone 10 reduction, but I did not have access to a gas kiln. Not many potters were firing to cone 6 in oxidation in the 70's. Thank you!
ReplyDeleteI hate to be the one to ask this but I am fairly new to the ceramic world. This will be my first attempt at making my own glaze. I have the chemicals to make a couple of these glazes, one is the blue green, I just need to know how to know how much water to add, and how do I know if the glaze is intended for brushing or dipping? Thank for any help and thanks for posting this information =]
ReplyDeleteJaneene
beanntony@aol.com
Janeene, I would start out by determining the weight of the chemicals. As a way of understanding, 10,000 grams with water will make enough wet glaze to almost fill a 5 gallon bucket. 5000 grams makes 1/2 that. 454 grams equals 1 pound. So 5000 grams make a little more than 10 pounds of dry chemicals. I start with 80% water by weight so if the dry batch is 5000 grams then weight out 4000 grams of water. Add the dry ingredients to the water a little at a time with stirring. When all is added and stirred, I run the mix through an 80 mesh screen 2 times. (80 mesh screen available at ceramic supply store.) Since you don't know how the glazes will turn out with your clay, firing, application, ect. I would start with a 300 or 500 gram batch (500 grams wet makes approximately a quart wet.) Make some test tiles of your clay and bisque fire them and apply the glaze several ways  dipping (one dip on whole tile and then after 10 minutes a second dip half way down.) Glaze should be the consistancy of heavy cream. To brush on the glaze should be a little thicker and you might add mineral oil to help with the brushing. Consult several books or the web for additional info that I cannot cover in this small space.
ReplyDeleteThank you for your help, my husband and I are trying to figure this out. If we wanted to make a 300 gram batch of the blue green, could you tell me how to convert the amounts. I have a digital scale but it measures in ounces, will that work with some conversions or do you recommmend I have a scale that measures in grams? Sorry to be a pest, thank you for your help.
ReplyDeleteJaneene
300 grams/454grams/pound = .66 pounds. 16 oz in pound. .66 times 16 ounces = 10.56 ounces. So 300 grams = 10.56 ounces which is total weight of the batch in ounces. If an ingredient is 30% of the batch then 30% = .3. .3 times 10.56 ounces is 3.168 ounces for that ingredient. Round it to 3.2 ounces for that ingredient. Do the same for all of the ingredients converting % to decimals and multiple the decimal equivalent times 10.56.
ReplyDeleteTerrific, thank you. I'll let you know how it turns out, looking forward to it =]
ReplyDeleteJaneene
FANTASTIC Red Rust Bottle! Thanks for all your work. Trish
ReplyDeleteThanks, Trish.
ReplyDeleteIs it possible, at cone 6, to leave the outside of the ware unglazed? I kind of like the look of it, wonder if it would be durable to leave it this way.. It's stoneware.
ReplyDeleteJaneene
Yes. The clay body that I mix has a very low moisture absorption rate (1%) when fired to cone 6 so very little water enters the fired clay body during use. If you are using the pieces to hold food, you may experience some issues with the pottery being washed and heat dried as in a dishwasher if your clay body absorbs a lot of moisture. The issues may be the crazing or spalling of the glaze as the moisture expands when heated. Best to try it and see what your results are.
ReplyDeleteI fired a batch of test tiles Sunday, specifically interested in the blue green, such a beautiful color! I'm going to try to post the pictures here. The blue green test tile is on the left. I fired it in my electric kiln, 1 hour on low, 1 hour on medium and then put the plugs in and let it fire to cone 6, (that took about 2.5  3 hours after switching to high). Fan was running until the end of firing and I shut it off. Seems all of the blue either burnt out or ? Not sure what happened to it, I got this green color, pretty but really wanted the blue.. The glaze seemed a bit thick when I dipped the tile, not sure if that may be the reason. The tile to the right was dipped into the blue green and then the top was dipped into a glaze thats called creamy, and I can see the blue a bit more in that tile. Any ideas where my blue went? =]
ReplyDeleteJaneene
Not sure how to post the pics, sorry
ReplyDeleteHi Terry,
ReplyDeleteGreat information posted here! One thing I will add to all this amazing information is clay body! After running test after test and tossing out a few good glazes I have learned a glaze that works on one clay body is not going to work on another. And one ugly glaze on porcelain might be beautiful on stoneware. Especially the iron reds.
enjoy reading the blog and thanks for posting all your hard work!
Sandy
Hello Terry, Thanks for the vast info on these tests. Have you tested a separate clear glaze or are you using a base of one posted minus the oxides?
ReplyDeletethanks
Robert
Robert, most of the glossy glazes will go clear with opacifiers or oxides. Are you looking for a clear C6? Terry
Deletecool colors where were the rest of them posted?
ReplyDeleteOn the blog. Summary page:
ReplyDeletehttp://wpapotters.blogspot.com/search?updatedmin=20110101T00:00:0005:00&updatedmax=20120101T00:00:0005:00&maxresults=21
Hi Terry
ReplyDeleteI've just started investigating Cone 6 glazes for some sculptural pieces and your blog with all your results has been a fantastic resource  thank you!
I'm trying to find the recipe for the #140 Hansen White you added to the top of the vase shown above. I've looked through the other pages but didn't have luck finding the recipe  if I've missed, can you please direct me to the right page or provide the recipe again?
Thanks again
Susannah
Susannah:
ReplyDelete140 Hansen Clear GA12 Cone 6 White
Custer Spar 0.2
Frit 3134 0.2
EPK 0.2
Wollastonite 0.2
Silica 0.2
Zircopax 0.1
Thanks so much Terry
DeleteSusannah
Hey Terry, Is the #18 correct? I think you want Barium Carb up to 19 not 1.9???
ReplyDeleteJohn, .19 is 19% so yes it is correct.
DeleteHello Terry, I was also looking at the #18 as was John Britt, I'm a newbe to mixing my own glazes. I see a few post about percentages, should they equal 100%, I'm coming up with a little over 800 for that receipe. Thanks...
ReplyDeleteMove the decimal to the right 2 places. Ex: .381 = 38.1% and .096 = 9.6%. If you add them all up, they equal 100% or 1.00. You convert decimals to percentages. It a recipe totals 105% for example, you can use it for batching purposes like that because it is the ratio of the different ingredients to each other that is important. For glaze #18, to make a 25 lb. batch you would take each ingredient times 25 lbs. Example for #18 : for G200 feldspar you would take .381 times 25 lbs. which would equal 9.525 lbs. To convert to lbs. and ounces take .525 times 16 ounces = 8.4 ounces. So G200 would be 9 lbs and 8.4 ounces. If don't understand, ask more questions.
ReplyDeleteI am looking for a purple cone 6 electric kiln "Glaze. Hope someone has one, I am currently working on some test tiles and can try more. Carol Fitzpatrick
ReplyDeleteThese glazes all come from John Post's site at 
ReplyDeletehttp://www.johnpost.us
You might want to consider giving him credit for developing these glazes. The tomato red glazes were developed based on a Pete Pinnell glaze and an article was written about them in clay times...
Gave John credit for some of the glazes some time ago (comments section). Glazes as you may know are posted many places sometimes with credit to the person who might have actually developed it and sometimes not. I have not taken credit for developing any of the glazes in these postings although I have modified some to create the effects seen. Taking credit is not important to me as much as sharing. I have attempted to help potters understand how to achieve certain glaze effects by providing the formulas, clay body, firing schedules, ect .
ReplyDeleteI want to test the #18 Jade Green on my clay body, but I'm confused. Are the ingredient amounts in grams or percentages? How do I convert these amounts into weights?
ReplyDeleteLynda, they are in percentages but don't always add up to 100% with the additions of oxides, but the ratios are the same. For Jade Green the first ingredient is G200 Feldspar at .381. For a 500 gram batch (total weight) you would multiply .381 by 500 grams to get 190.5 grams of G200. Hope that answers you question.
ReplyDeleteIs the Jade Green a glossy glaze finish or matte or Semimatte? Charlene
ReplyDeleteSemimatt if I recall.
ReplyDeleteHello, would someone be so kind and explain to me what does it mean in de formulas that you give: 0.381,0.19,0.231,etc. I usually find them in porcentaje. Thanks!
ReplyDelete0.381 is a decimal. Move the period two places to the right and you will get it as a percentage. 38.1% However it you were batching a glaze to make 2000 grams total in the batch, you would multiply 0.381 times two thousand grams to get 762 grams of that material.
DeleteVery nice colors. I live in Norway and wonder what cone 6 is. What is the top temperature?
ReplyDeleteIt is not possible to get the ingrediense OM#4 Ball Clay in Norway. What can I use instead? Is it a white clay?
ReplyDeleteCone 6 is approx 1220 degrees Celsius. OM#4 is known as Old Mine Kentucky ball clay. Follow link: https://digitalfire.com/4sight/material/om_num_4_ball_clay_1098.html Not sure about ceramic suppliers in Norway.
ReplyDelete