Returning to my regularly scheduled clay blog after going off topic the other day…
I really want to expand my glaze palette and am searching for some fun translucent candy colored bright eye popping color to highlight the texture on a lot of my new hand built pieces. I’m testing glazes in oxidation (electric kiln for you non-clay people) at cone 6 (temp 2232 degrees F) on a white stoneware clay body called Ash (available from Mile Hi Ceramics).
The glaze properties I’m looking for include:
- a tight fit (no running off my ware)
- translucency
- vibrant color
- stable – no crazing, pitting, crawling or pinholing
- food safe
- cost effective and reasonably safe raw materials
Colors I’m working on:
- Chartreuse
- Pink
- Orange
- Violet
- Robin’s Egg Blue
I already have a celadon, clear and white glazes in my repertoire. If you’re a clay person, you probably already know that the colors I’m striving for are hard to get in the properties I’m looking for at higher temperatures outside of maybe commercial glazes (I could very well be off the mark though since I consider myself a novice glaze chemist) . These colors are widely available in low fired earthenware pottery. But, once you move into mid-range and high fire, many of these colors burn out mainly the pinks, reds, yellows and oranges. Or they require a reducing (gas kiln) atmosphere in the case of reds and oranges.
To achieve color in glazes one can use oxides or manufactured stains. There’s a few stain companies out there such as Mason, Cerdec-Degussa inclusion pigments, and Blue Heron (can’t find company website) – and maybe more that cater to commercial manufacturers of ceramics & pottery. Oxides include copper carbonate, cobalt carbonate, iron oxides, chromium, manganese to name a few.
So, for this glaze testing cycle, I chose to test pink and chartreuse colored glazes.
Glaze Test Recipes
Note: Stain is good up to 2300°F No Zinc in Glaze Needs a high calcium glaze (provided by the wollastonite) |
Note: Based on my research, tin is a necessary ingredient for chrome to develop pink |
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Note: Stain is good up to 2300°F Can be used as a body stain Can be used with or w/o zinc in glaze Results – turned chartreuse at max 10% colorant added Matte at 10% |
Note: High alkaline glaze with no tin |
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What you see isn’t always what you get when it comes to glazing!
I did a 6 part color progression test for each of the test glazes (one of the recipes isn’t listed as I added it at the last minute) using Ceramic Spectrum by Robin Hopper, pg. 187 as my guide.
Only 1 of my glaze tests turned out the way I expected!
The others are all duds unless you consider drab olive green pleasing… so back to the drawing board me. I actually anticipated that 2 of them would fail after further research & AFTER I had already mixed up the test batches, but fully expected Glaze #1, 2 and 3 to turn out. I also realized last night that I misread the glaze I really wanted to try for glazes #1 and #5 and used a different one than intended – doh. #2 is pretty – but it’s an ineffective way to get blue when I could simply use cobalt carb. The chartreuse stain was tested on a semi matte base glaze, which I’m not sure I like. It’s looks more mustardy yellow than acid yellow-green. A gloss may be better – so I’m going to keep on testing before trying a new stain.
I thought I had fully accounted for how all the different chemicals & minerals were going to react in the kiln, but I was wrong. I became painfully aware of the fact after I downloaded 2 different trial glaze calculation programs. I’m testing Insight (free trial for 2 months) and Glaze Master (also available as a free trial for 2 months). I really like Insight since it felt pretty intuitive to use – but I really need to read the instruction manuals to really use both of the programs to their full advantage before making a purchasing decision. There is also a free glaze calculation program called, appropriately, The Glaze Calculator, that I should probably investigate. Here’s a bigger database with different glaze calculator programs that are available.
Since I’m really looking for stable glazes to use on surfaces that come into contact with food, certain chemicals are off limits and I really need to read up on glaze expansion, alumina/silica ratios and while I’m familiar with limit formulas, it’s only starting to make sense me. I really wish I had paid more attention in chemistry class.
On one hand, I feel like I’ve got just enough information to be dangerous or simply very frustrated – and liken myself to throwing darts in the dark hoping to open the kiln and find success with any luck. On the other hand I’ve been doing so much reading regarding glaze chemistry that I realize how much I have to learn.
Meanwhile, a fellow clay person and Etsy Mud Team Member, Eleanor pointed me in another new direction – that of lanthanides or rare earth minerals as colorants for glazes. She pointed out these 2 articles Rare Earth Colorants by Max Campbell and Chris Keane and Exciting New Transparent Glaze Colors Using Lanthanide Colorants by David Pier. Although, after a little bit of research, Laguna clay has stopped distributing Praseodymium which creates the greens and yellows due to steep increase in price (so this may be a dead end)- but there’s always Praseodymium yellow Mason Stain #6408 to use as a substitute.
Update: I just found this article by Tony Hanson that includes a recipe as a starting point for making a pink ^6 glaze. My problem? In addition to not having zinc in a chrome/tin glaze, there can be no magnesium. If I had seen this little tid bit before (and it clearly states that in the Mason Color Chart which I neglected to see even though I’ve read the damn thing 100 times) I would have realized that my test recipes above contain Magnesium! Doh
Back to chemistry class for me!
~Cynthia
14 Responses to “Dismal Cone 6 Glaze Test Results”
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Wow, you work fast, I am impressed with all your glaze research and testing. I like the chartreuse. Anxious to see the gloss.
Ouch! I would be right with you on the frustration!
I like the 4th and 5th tiles on the chartreuse. To help the pinks burning out – have you considered applying a clear glaze on top? Sometimes it keeps the reds red.
Mornin’ Cynthia
“Clay and Glazes for the Potter” by Daniel Rhodes has been a great help to me. His recipes always seem to work. When i was doing Cone 6 glazes, it was his guidance that enabled me the “break-thru” needed to go beyond frustration !!!
His glaze #18 is a great base. Takes oxides and color well. It is matte but with his #15 sprayed over it the overall piece comes out glossy.
Ought-a mention here: i measure all glaze ingredients by 1/8th tsp’s. And usually divide recipes by half’s or fourth’s as my elect kiln is small and usually fire 1-2 pieces at a time. Also, my “Cone 6″ temperature is: 2167 degrees F. (Some resources list this temp as ^6; others list it as ^5 !!!)
So! Four [1/8ths tsp] of Titanium added to Rhode’s #18 (halved) with his #15 sprayed over it will give you yellow — a very sweet yellow. Consistently.
For a very light blue: add 1/8th of [1/8th tsp] copper oxide plus 3.5 [1/8th tsp]Tin Oxide to Rhodes #18 with #15 sprayed over it.
For deeper blues play with the ratio of the tin oxide and the copper oxide. (Discovered copper carbonate – after – i switched to Raku glazes from the Cone 6 – and i like this better — but the recipes above are “for sure” colors when still using the oxide.)
Haven’t mastered the oranges + reds yet, so can offer no help there.
U.S. Pigment Corp carries all the lanthanides – rare earth metals. Saheeb is the person to talk to there. Nice fellow – very helpful.
Have tried Praseodium. Wasn’t all that impressed with the results and found better yellows + lime greens with titanium !!!
Very few of the “text” books (which you’ve already mentioned) give much info on Titanium so it was a discovery much by accident in a few of my experiments.
Potassium Dichromate is more useful for producing oranges, yellows + reds than Praseodium but i hesitate to mention this for according to all info i’ve read — it’s fumes are highly toxic. And too while i have achieved a sorta orange with it, haven’t gotten the red’s it’s spoze to produce!
Guess i’ve been talking too much, eh?
Sorry.
Just so tickled to help if i can.
Hugs
Chae
Thanks Linda!
Hey Lisa – I was just reading about different methods of using stains and the one you mention was right there! I also just found out that there can be no MgO in the glaze or it will burn out. Guess what? Both glaze recipes contained magnesium! Those 2 you mention are also my faves.
Funny you should mention the Rhodes book, Chae – it’s on my list to borrow right now! Thanks so much for all your information too – very helpful!
Thank you for sharing the results of your hard work! I did some not-so-exciting tests of colorant variations for a favorite glaze and haven’t gotten to photographing them yet… and I’ve been planning to do several line tests for 35 tiles in all… this gives me some inspiration to get in the lab and keep it cooking. Unfortunately they are c.10 reduction, so the results won’t contribute to your work… wish that was the case!
My head hurts.
Another glaze program is Hyperglaze written by Richard Burkett in San Diego. I don’t believe he has a free trial version though.
The web site is: http://www.hyperglaze.com/
Wow, there’s a real science to this isn’t there? This is why I want to take up classes – to learn the scientific side of ceramics.
Welcome Julie and thanks for your comments! In some ways I find glazing to be the unglamorous part of ceramics but it’s also exciting when things turn out. The Zen master side of me is say, “little rabbit, all is not lost. Look at what you have learned today.”
I do fire at ^10 – but I use the Colorado Potter’s Guild glazes. I understand the theories behind reduction, but at this point, I’m using tried and true recipes.
Mine too, Janet!
Thanks Anne, I think I looked at that one – but I gotta be able to try it out first.
Linda, I really have to delve into this head first myself or take a class for the structure. I’m going to try the former and see if I can get a better grasp on it. I did a quick look at some of the ceramic programs at some local community colleges, but didn’t see any glaze chemistry classes. I might have to check into CU if I decide to go that route, or find a workshop somewhere.
When I was in every chemistry class in college (I’d never taken chemistry in high school and became in effect a chemisty and biology major) each teacher would bring out the fact that we all use chemisty every day of our lives even if all we do is boil water. (Heat being the catalyst!) For me, it was an eye opener. I remember back in the 60′s, I took an informal gathering of ceramics and the discussions we had about when things could and couldn’t be fired by the teacher because of using full kilns and what couldn’t go in with other stuff. Not that it would mean anything today, just that I thought it had ever been the bane of ceramics people to get the right glazes and not have other stuff in the kiln that were the ‘wrong’ glazes, etc.
As for not seeing what’s there! I do that all the time! Don’t you just hate that!? I do. It makes me feel like the biggest duffus in the world when I finally see something I’ve skipped right over or totally didn’t see in the 101th reading. Oh, that is frustrating.
Not being a clay person, I have SUCH a profound respect for the craft. This post exemplifies the tedious trial and error element of the process that many may not realize when looking at a pretty finished product. I took just one college ceramics class, so I know the tip of the iceberg of how unpredictable glaze can be. It’s such a different world from mixing paint on a palette where what you see is what you get. I wish you the best of luck in finding the colors you are really looking for and I can’t wait to see what you create with them!
I have a suggestion before you get too far along! Know the thermal expansion of your clay body before you test a trillion glazes(learned this the hard way) It dosen’t matter how brilliant a pink you get if the expansion isn’t right for your clay it will craze every time. Start at pg.67 in Mastering Cone 6 Glazes. It is as all aspects of ceramics time consuming but once you have it and your working away in insight trying to develop a glaze it gives you the expansion so you know immediately if crazing is going to be a problem. I have some tests to mix myself tonight! Good luck!!!
PS sometimes a clay company can give you that info – give them a ring.
You have been so busy with researching and testing the glazes and I’m LOL at what Janet said!
eek, Cyn it must be a very complicated and time consuming process to mix the glazes and test all those samples!
You are absolutely right, Mary! I did a couple of presentations to a local high school for career day and that was one of my points. I was one of those kids who struggled with algebra & geometry (though I forced myself to take it so that I’d have the pre-req for college). I kept thinking, why do I need this?? “I’ll never use this again”. Well, lo and behold, I need math, chemistry and found geology incredibly useful for my ceramic endeavors.
As for not seeing something right in front of my eyes – I did it again last night!
Thanks Jessica for the comments – long time no see! Lol, I sometimes think that I should switch mediums because it would be easier. But, I know that’s not true – there’s a whole other aspect of 2d work that requires attention, study and practice.
Kris – welcome! Funny you should say that about the clay’s thermal expansion – I was just reading up on that very section in MC6G last night. I’m calling Mile Hi Ceramics this morning when they open to find out what the expansion is for both the clay bodies I use, Ash (a white stoneware) and Aspen (a ^6 porcelain).
You can say that again, Lynette! I’ve got a ceramic poem going through the back of my head right now that goes to the tune of “Twelve Nights of Christmas”, only the title is “Twelve Nights of Testing”