Pete's Weathered Bronze (Green)

[George Lewter]

Recipe Name:  Pete's Weathered Bronze

Cone:  6-9     Color:  green bronze
Firing:  Oxidation     Surface:  Matte

Amount     Ingredient
60          Nepheline Syenite
20          Strontium Carbonate
1          Lithium Carbonate
10          Ball Clay--Old Mine #4
9          Silica

100         Total

               Additives
5          Copper Carbonate
5          Titanium Dioxide

Unity          Oxide
.047           Li2O
.334           Na2O
.106           K2O
.009           MgO
.028           CaO
.475           SrO
1.000          Total

.577           Al2O3
.003           Fe2O3

2.973           SiO2
.005           TiO2

5.2          Ratio
8.8            Exp

Comments:  Metal Marks
Hesselberth leach tested for copper and averaged 5 mg/l which he considered very stable for the amount of copper in the glaze.
Needs a full cone 6 down. Sometimes will pinhole.

Relatively high coefficient of expansion.

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Calculations by GlazeMaster™
www.masteringglazes.com
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Example posted by Michele Hartung

[Barbara Hanselman]

 

I had to stop using the Weathered Bronze at the art center where I teach because they only fire to cone 5 and don't slow cool.  The WB really pin holed terrible and just didn't look good at 5, so instead we mixed up this glaze below and although the coloring is more to a turquoise than a green we have no pin holing but the same butter finish as the WB.

Pete’s Seafoam ^5/6

9.6%           Ferro Frit 3134

51.3%         Feldspar-Kona F4

25.5%         Strontium Carbonate

12%            EPK

ADD:

5.0%           Copper Carb

5.0%           Titanium Dioxide

2.0%           Bentonite

This is Pete Pinnell’s strontium light matte turquoise

[Barbara Hanselman]

My Weathered Bronze fires differently than yours at 5/6 -

Weathered Bronze (Frog Pond Green) ^5/6

60%            Nepheline Syenite

20%            Strontium Carbonate

1%              Lithium Carbonate

10%            Ball Clay-Old Mine #4

9%              Silica

ADD:

5.0%           Copper Carb

5.0%           Titanium Dioxide

2.0%           Bentonite

This is also a Pete Pinnell’s strontium glaze.  Needles to say, the fired color of both the Seafoam and Weathered Bronze are almost identical but the Seafoam glaze really goes on nicer and seems to fire more evenly. 

[Barbara Hanselman]

Pete's Seafoam

[Jan Wallace]

Thanks for the recipe and photos. Its really nice how the Weathered Bronze works with the contrasting darker, shiny glaze. Nice pieces. Barbara, what is the best way to apply this glaze please?

[Barbara Hanselman]

I brush on glazes when multi-glazing and pour the insides but dipping also works.  I like the way the weathered bronze fires and looks when applied unevenly, so brushing and layering in certain areas makes that easier than dipping.

[Jan Wallace]

Thanks Barbara, I will keep that in mind.

[0ibbwdyhdge9l]

Hi All.  Can someone send me a firing schedule for the pinnell weathered bronze? COne 6, skutt electric.  I would appreciate it!

[Barbara Hanselman]

The best I can do is give you this article by Pete which I base my slow cool firing on...

 

Of Cones and Kilns by PETE PINNELL

 Let's say I'm baking a fancy layer cake. I mix the batter in a large bowl, preheat the oven to 350°, pour the batter into three round cake pans, and place them in the oven. Now, let's say I remove one of the pans after 10 minutes, the second after 25 minutes, and the third after an hour. All three layers of my cake look alike, right? No? Why not? After all, I fired (oops-cooked) all of them to the same temperature, right?

The reality, of course, is that the first one would be under-cooked, the second one would be about right, and the third one would be over-baked-possibly burned. As all of us who cook know it's not just the temperature that counts; it's also the amount of time that the food is exposed to that temperature.

The same thing is true of our ceramic firings. It's not just the temperature we program into the computer control on our electric kilns, it's the amount of time that the kiln takes to reach that temperature, the amount of time it holds itself at that temperature (what's known as "soak" time), and the rate at which the kiln cools. All have an enormous effect on how "done" our cake (I mean "artwork") is.

How "done" something is comes down to two variables-temperature and time-and both are equally important. When combined, time and temperature are known as "heat-work." Finding a way of accurately measuring heat-­work was a matter that frustrated potters and, later on, pottery managers, for centuries. The man who came up with the best solution was a German scientist named Hermann Seger.

In 1886, Seger published a treatise entitled "Pyrometers and the Measurement of High Temperatures: Standard Cones." In it, he outlined a system of cones made from the same materials as are found in standard porce­lain glazes. These cones respond to heat-work

in the same fashion as the pottery that is being fired in the kiln. In short, cones were-and still are-the best way to observe heat-work in action (during a firing), and to produce a re­cord of the total heat-work that can be easily read after a firing.

Here's how the time/temperature balance works. If the kiln fires slowly, it will not need to reach as high a temperature to achieve a particular level of heat-work. With more time, you don't need as high a temperature. Conversely, if a firing is very rapid, then it will have to extend to a higher temperature to get that same heat-work. For example, brick manufacturers fire quite slowly, and may reach "cone 6" at a temperature almost 100° lower than a hobby potter firing quickly in a small kiln. A cone pack factors in "time" in a way that a pyrometer cannot, ultimately providing a much more accurate picture of the "temperature" the work reached.

Why am I telling you all of this? Because ev­ery time I publish a new cone 6 glaze recipe in Clay Times, I get one or two letters along this line:

"Why do you keep giving us cone numbers? No one uses cones anymore, and when you give us just the cone, then I have to look up the temperature so I know what to program into my computer controller. Since most of us use controllers now, why don't you just give us a temperature? Join the 21st century!"

If you've been paying attention thus far in the article, you now know why: knowing tem­perature alone doesn't provide an amount of heat-work. It's like saying, "bake the cake at 350°." Yes, but for how long?

The interesting thing about cones is that even they don't give us all the information we need. Seger's cones provide us with a good way to

measure melting, but that is only part of the story with kiln-firing. Melting occurs on the way up in the firing, and continues during the soak time. However, what largely governs the visual characteristics of many contemporary glazes is the kind of "phase separations" that occur within the glazes. These separations begin to occur at the end of the soak, and con­tinue to form as the kiln cools. As it turns out, cones don't measure how quickly the kiln cools, and the cooling rate is a critical piece of information for controlling glaze color and surface, especially in electric kiln firings.

Anyone who has ever taken a glaze class from me knows that I love to talk about phase sepa­rations, both for the useful, practical informa­tion, and also because it sounds like cool "Star Trek" talk:

Scotty: "Captain! There's a phase separation occurring!"

Captain (soothingly): "Let it soak, Scotty. Let it soak."

When we talk about "phases" of matter, we're merely talking about the different form a sub­stance can take at varying temperatures. Take, for instance, our old friend H₂0. Below 32° F, it's a solid (ice). Heat it up a little and it be­comes a liquid (water). Heat it up a bit more, and it becomes a gas (steam). We call that lowest phase "the solid phase," the middle one "the liquid phase," and the last one "the gaseous phase." As it happens, virtually all non-organic substances exhibit these three phases, and do so at widely different tempera­tures. So in any given glaze, we might find some things in a liquid phase, some in a solid phase, and some in a gaseous phase. It's this variety of phases that provides the visual and tactile qualities that cause us to look at glazes and say, "Ooooh!"

 

Glass-whether in a window or in the form of a clear glossy coating on a pot-is (techni­cally speaking) a liquid. It has the molecular structure of a liquid, even though it doesn’t flow at room temperature in the way we would expect a liquid to. The molecular structure of glass, like any liquid, is described as “amorphous,” meaning “without form.” In other words, that “structure” is random, with no discernible pattern. Scientists call glass a “super-cooled” liquid. When glazes mature, they completely (or almost com­pletely) melt, entering this liquid phase. Some glazes then begin to change, with parts of the glaze separating out to form micro­scopic crystals. Crystals are merely molecules that have reoriented themselves into dis­cernible patterns that are repeated over and over. We see and feel these crystals as matte or crystalline glazes, or as color shifts such as the titania crystals that form the beautiful blue color we refer to as “rutile blue.” This kind of separation is known as a “liquid/ solid” phase separation.

In other glazes, parts of the liquid glaze may separate out to form a secondary glass that floats as little globules in the main glaze, act­ing sort of like the mix of oil and water that occurs in a recently-shaken bottle of salad dressing. These little glass globules can re­fract light and cause a variety of effects, from translucency and opacity, to the wonderful opalescent qualities of a Chinese Jun blue or the brilliance of a copper red. This second kind of separation is called a “liquid/liquid” phase separation (and if that doesn’t sound like “Star Trek” talk, I don’t know what does).

Every so often I’ll get an e-mail along this line:

“Why can’t I find a good matte glaze recipe? Every recipe I try is just glossy, or insipid, or just plain nasty. I want a soft, velvet matte. Are people keeping these recipes secret? Are you and the other glaze gurus leaving out secret ingredients in order to vex us beginner potters?”

In the case of the glaze recipe this woman was writing about, the fact was that I did leave something out. I didn’t say anything about cooling rate. I wrote back, and found out that she was using a computer control to fire her kiln to a preset temperature for “cone 6.” I asked her to put a cone pack in the next firing, and we found out the kiln had only reached cone 5 (and barely that). Besides that, the controller program she used just turned the kiln off after reaching temperature, and her kiln cooled too quickly for crystals to form in the immature glaze. The “secret ingredient” she was looking for wasn’t missing from the recipe, but from the firing. She needed to slow down her firing, take the kiln a bit hotter, and to “fire down” enough to allow crystals to grow.

Her next firing was perfect, and she got ex­actly the glazes she wanted, though she re­ported a little more running. “My beautiful new glazes ran off the edges of my lids and stuck them all down.” Yes, glazes can cer­tainly move more when you give them more time to do so. That’s what makes ceramics so much fun-there’s always another problem to solve.

6 (which I define as a large cone 6 touching down, and cone seven beginning to bend). Thermocouples vary, so your final tempera­ture may need to be adjusted slightly to reflect this difference. This firing cycle takes about 12 hours from room temperature to shut off, which is faster than some of the cycles I’ve seen, and slower than others. If you’re mak­ing large, thick-walled stuff, you might want to slow down the first and second segments. If you want more matting in your glazes, you might want to slow down or extend the final “fire down” segment. It’s easy to customize a cycle to give you the best results from your glazes in your kiln. You should feel free to alter this cycle to best fit your work.

Segment 1

100°/hour to 200° F

Segment 2

400°/hour to 1950° F

Segment 3

100°/hour to 2150° F  (MLAC had to raise this to 2169 F for a cone 6)

Segment 4 (fire down)

150°/hour to 1700° F Off

 

Computer controls are terrific things, but I always include a cone pack in the firing so I can check up on things as the firing pro­gresses, and have a record of the total heat­work when the firing is over. So, even while we are all moving into the 21^st Century, it’s comforting to know that some things from the 19^th Century still work just fine, thank you very much.

You can write to me about cooking (or other matters) [e-mail].

What almost all phase separations have in common is that they take time to form. Mol­ecules have to move around in the glaze in order to take on these new forms. If insuffi­cient time is allowed while the glaze is still fluid, then these phase separations simply won’t occur. This isn’t generally an issue in gas kilns, because they tend to be large, with heavy posts and shelves, and thick, well­ insulated walls; they naturally cool slowly. Electric kilns, on the other hand, have thin walls that provide little in the way of mass or insulation, so they tend to cool very quickly after they are shut off. In this kind of kiln, firing down can become the only way to slow down a cooling cycle enough to allow phase separations enough time to occur.

The controllers I have used can be pro­grammed to give you just about any firing or cooling rate you want. What they don’t do terribly well is estimate the total amount of heat-work that will occur during the firing, so while you may enter “the temperature” that’s supposed to provide cone 6, you may end up above or below that, depending on the speed of the firing. When you add on soak time or a longer cooling cycle, you are also adding more heat-work, so you may need to adjust your top firing temperature a bit to prevent over-firing.

Pete Pinnell teaches at the University of Nebras­ka-Lincoln. He has been a potter for many years and has numerous exhibitions and workshops to his credit.

 

CLAY TIMES November/December 2004

Volume 10, Number 6

 

[0ibbwdyhdge9l]

Barbara - Oh Thank You!  Right from the horses mouth so to speak.  Joanna

[Barbara Hanselman]

You may have to tweak the final temperature for your own kiln as we had to do at Main Line Art Center but otherwise, this seems to work well and is a little shorter in time than the one suggested in Mastering Cone 6 Glazes. 

Barbara

[Patricia Bridges]

Here are 2 samples of Weathered Bronze. I fire in an Amaco Excel Select Fire kiln- Controller is made by Skutt. This is the result on a clay body with manganese specks. Standard 112. Standard Cone Fire Program Cone 6. I have an Environvent. Looks the same at Cone 5 + 7 min hold. All programmed in your Skutt controller.  Thicker goes greener - thinner goes blackish/smokey.

Th

Bridges Pottery Butter Dish - Weathered Bronze + clear coat on interior

Bridges Pottery Teapot .

Weathered Bronze (Frog Pond Green) ^5/6

60%            Nepheline Syenite

20%            Strontium Carbonate

1%              Lithium Carbonate

10%            Ball Clay-Old Mine #4

9%              Flint

ADD:

5.0%           Copper Carb

5.0%           Titanium Dioxide

[Barbara Hanselman]

Love both these glazes!  This Weathered Bronze or Pete's Seafoam (I can't remember which one I used) is on Miller Laguna #40.