rctc cone 4 initial tests

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Cone 4 Neutral Glaze Test Notes

Tim Carlson

October 16, 2011

Conventions in these notes:

Here in these notes, I take a break from the standards I normallyuse. These notes are primarily in units by volume except where Ispecify by weight. More specifically, only the cone 4 eutectic testsI made are actually in parts by weight; all others are by volume toenable quick generation of tests. The purpose of doing tests in thismanner is to simplify the initial series of tests since I am starting fromscratch. Had I a base glaze to start from, everything would be byweight; note that once I suspect that a glaze could be formed fromthe correct proportions, the units will be converted to proportions byweight. Also, none of these glazes are normalized by molecular unitynor by 100g recipes; instead, these recipes are listed by parts since

calculations which involve the Natural numbers are much simpler. Aswell, at RCTC, these glazes were fired to Cone (∆) 4 in a neutral /lightly reduced atmosphere.

1 Introduction

I find myself in the predicament that I am a traveling teacher, essentiallyhaving been transient in my employment locations over the course of mycareer. Interestingly, this year, the studio I find myself attached to is in astate of transition.

The events have transpired in this way: last school-year, the studio oper-ated a ∆10 reduction gas fired kiln as well as an anagama and a wood/saltkiln, all principally ∆10 reduction. Over the summer there was a change toa low fire clay body with an upper limit for firing of ∆4. The gas fired kiln isnow for firing to ∆4 in a neutral atmosphere. So on my arrival at the school

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in the Fall, I was greeted with the opportunity to learn and work at a much

lower temperature than I have ever before. Of course, my preoccupation withglaze and texture has lead me to try many new sorts of things! Note that as Iam unaware of the impetus for these changes, but I recall the idea that peopleare trying to use less energy overall as part of a responsibility trend; therehave been enough studies completed which mark the significantly less energyusage for firing to cones below ∆10. See www.studiopotter.org Volume 5, No2 by Val Cushing in November 1976. Note that I am enthusiastically tryingto take advantage of a new opportunity to learn.

Included below is a mention of Google pointing me to a valuable articleon CeramicArtsDaily.org, but I also feel the need to mention another siteGoogle directed me to which is a database of phase diagrams (a technical

listing of eutectics). The site is www.sgte.org/fact/documentation. With theavailable data on this website, there should be plenty of ideas for line blendtests and for triaxial blends for investigating new glazes and glaze bases.

I hope that this collection of notes provides the opportunity to followalong with my thoughts and efforts during my year at this new studio.

Since I am presented with this unique opportunity, I begin by takingadvantage of the sparse availability of different glaze bases at the studio inthe firing range of ∆4.

2 Eutectic Tests

The first thought which occurred to me is to try and find a eutectic blendwhich has a melting point at the range which we were firing to. Googleprovided me with this trusty Ceramic Arts Daily article and an idea that Icould try! The eutectic listed in the article is:

Eutectic RecipeAlumina Oxide (Al2O3) 14.75Calcium Oxide (CaO) 23.25Silica (SiO2) 62

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Since Calcium Oxide is not readily available for use in a glaze, it wasnecessary to convert this formula to a useful form, i.e. substituting the useof Whiting (CaCO3) for the Calcium Oxide. As well, I chose to use EPK(Kaolin) as a substitute for the Aluminum Oxide. But the chemistry of these

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http://www.studiopotter.org/articles/%3C?=$pubbackurl;?%3Eback_1#Vol5No2


http://www.sgte.org/fact/documentation/FSdata.htm#overview

http://ceramicartsdaily.org/ceramic-glaze-recipes/glaze-chemistry-ceramic-glaze-recipes-2/how-glazes-melt-in-search-of-the-elusive-eutectic/

http://ceramicartsdaily.org/ceramic-glaze-recipes/glaze-chemistry-ceramic-glaze-recipes-2/how-glazes-melt-in-search-of-the-elusive-eutectic/






substitutions is the real trick.

It was necessary to convert the weights listed in the recipe above to anequivalent number of molecules, or more precisely in chemistry terms, moles.Then, using the EPK as the first ingredient, you can find that 37.309g of Kaolin provides 14.75g of Al2O3 AND provides 17.353g of Silica as well as abunch of H2O molecules which are neglected since they (hopefully) will bereleased in the firing. Then with the assumption that Whiting is the onlysource of Calcium (meaning that EPK does not contain Calcium), we canfind that 41.518g of Whiting provide 23.25g of Calcium Oxide, which requiresonly the additional 44.647g of Silica to complete the recipe using ingredientsfound in nearly any studio. This recipe is essentially the one listed below asthe Eutectic Base Glaze, with the additional modification of normalizing my

recipe to EPK=35g. Notice that this section has all the weights specified bygrams.

Eutectic Base

Eutectic Base GlazeKaolin 35gWhiting 39gSilica 42g

As can be seen in this picture, the mixdidn’t quite melt. It did begin to fuseand even on the edges where the glazewas thin, started to melt. The edgemelt began to interact with the mixand started to show a brown/greenmatte appearance, likely due to the

interaction of the clay/mix interface. I suspect that this mix is right onthe edge of melting at the temperatures we fired to; not just because of theclay/mix interface action, but the hardness of the fusing and the cracking of the fired mix behaved much like the Sperry Mud Crack Glaze consistingof a 50/50 mix of Neph Sye/Magnesium Carb in a ∆10 firing.

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Eutectic with Yellow Ochre

Eutectic with IronKaolin 35gWhiting 39gSilica 42g

Yellow Ochre 20g

As shown in this picture, with the ad-dition of 20 parts by weight of Yel-low Ochre, a fine satin/matte surfaceis produced, though the color is of a

green chocolate. This additional in-formation leads me to think that

the iron is behaving as a flux or activator in this glaze, just enough to pushit over the edge to melt. There also appears a possibility of light crawlingwith this glaze. Would titanium act as a viscosity stabilizer for this glaze?Or would it cause the texture to change drastically? Maybe for the better?Would Magnesium reduce the surface tension likely due to the high Calciumcontent?

This appears to have potential for more tests, especially a runny-nesstest, i.e. how it behaves on a vertical surface and the texture it achieves.

Eutectic with Yellow Ochre and Strontium Carbonate

Eutectic, Iron+StrontiumKaolin 35gWhiting 39gSilica 42g

Yellow Ochre 20gStrontium Carbonate 20g

This mixture shows the deep richbrown of a high iron glaze and also

crawls as if it were a fake-ash type of glaze. Where it is thin, it is a greenishbrown, much like a fake ash glaze.

The tonal depth of this glaze with respect to it’s thickness seems to lend it

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a pleasant quality. Would rutile lighten the color and possibly stabilize it a

little more? This one is definitely on the list for more tests since a nice fakeash glaze would work nicely with raised slip decorated items. Try addingMagnesium Carbonate, or substitute Dolomite for some of the Whiting.

Other Questions

As I made up the glaze recipe, I began to wonder about the possibility of substituting other elements for the Calcium, such as Barium and Strontium.Since Barium is unavailable, I think an attempt to use Strontium as a re-placement for part or all of the Calcium is an acceptable idea at a 3 : 2proportion from the consideration of the molecular weights.

This presents a good opportunity for

3 ∆10 Crystalline Base Glaze at ∆4

Another idea which occurred to me was to use the recipe for a ∆10 crystallineglaze at ∆4 temperatures and see what happens. So far I have neglected totake pictures, but listed below is the recipe along with my observations andquestions for revisions.

The texture of the glaze is a drymatte with chunks of un-fluxed zinc

oxide in it. The color is quite an at-tractive yellow, hence the suggestionof ‘canary’; and there appears to besome motion in the surface of thisglaze showing that ∆4 is a great tem-perature for the maturation of this

Underfired ∆10 crystallineRenamed: Canary?

Frit 3110 55gZinc Oxide 35gSilica 10gTitanium 10g

Rutile 4g

glaze and that the time at temperature is fantastic in that the viscosity doesnot decrease to a level where the glaze becomes so fluid that it runs signif-icantly. I’m thinking the texture is possibly from the formation of crystalsrather than the the incomplete melting of the glaze.

Some directions I would like to take are:

• add Lithium Carbonate (5g)/100, (5g)/100 TiO2 and (2g)/100 of Rutileto the current batch

• Try a simple reduction of the Zinc Oxide down to 25g or even 20g

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• try iron oxide of various levels

• for color,try: copper carbonate

ilmenite?Manganese?cobalt?tungsten sulfide??nickel carbonate?

4 Line Blends

Here, I made attempts to create quick and dirty line blends of basic materialswhich were available at the time. Soon I will do more tests of line blends(always quick and dirty, using volume portions for initial tests), but I willalso be including a section of triaxial blends as well.

I hope to stumble across some good possibilities for base glazes using theseline blends. Of course, there’s always the hope that these tests can producea rich, wide range of a color palette using only the simple metal oxide colorinducing ingredients of Iron, Rutile, Ilmenite, Titanium, Copper, and themodifiers of Calcium, Magnesium, Lithium, Tin, Zinc, and Strontium. I dolike to use other ingredients, but I currently find the others to be unavailableat the studio.

One of my specific goals is to produce a deep iron red; the ideas fordeveloping such a glaze will be one of my first attempts with a triaxial blend.

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Frit 3134 and Ravenscrag Slip.1

Listed as“Test Letter”,(Frit 3134, Ravenscrag Slip)

A,(1,0) B,(3,1) C,(2,2) D,(2,3) E,(1,2) F,(1,3)

Comments and Notes.

• For Test A, I wanted to see how Frit 3134 behaved simply on it’s own.As a glaze, it is a little milky and blue, but it crazes badly. The crazingis most likely due to the high linear coefficient of thermal expansion.In general, not too bad except for the crazing.

• For Test B, the blend is 3 parts Frit 3134 and 1 part Ravenscrag Slip.As a glaze, it has definite possibilities. It also has a milkiness andrunny-ness associated with it. One thing which is not really noticeablein the picture is the slight pitting occurring in the surface of the glaze.

• For Test C, the blend is 50-50 by volume. This is a cream coloredsolid glaze which might be reasonable for coloration by metal oxides.It appears to be stable, slightly runny, though it also seems to have aslight pitting occurring in it.

• For Test D, the blend is 2 parts Frit 3134 and 3 parts Ravenscrag Slip.Here the glaze seems to be much more stable, with a milky film over

1Remember that this is in proportions by volume!

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sections of the surface. Might be very interesting with metal oxides in

it; this blend should be explored more.• Test E had 1 part Frit 3134 and 2 parts Ravenscrag Slip. The milkiness

occurred where thick with hints of blue, but where thin, appeared green.Is the green due to iron interactions from the clay body? Also, not quitenoticeable in the picture, there seems to be a satin surface characteristicwhich might be worthwhile to explore as well.

• And Test F has a boring pale green satin surface with some appearanceof surface pulling and cracking, as if the glaze melted, but not quitewith everything dissolving into the melt. Reminds me of pale greensuede.

Other Questions.

Possibly it might be worthwhile to

Bone Ash and Alberta Slip with just a hint of Frit 3110.

Listed as“Test Letter”,(Bone Ash, Alberta Slip, Frit 3110)

A,(1,0,0) B,(5,1,1) C,(4,2,1) D,(3,3,1) E,(2,4,1) F,(1,5,1)

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Comments and Notes.

• Test A contains straight bone ash. I know that it doesn’t melt at ∆10,but I couldn’t help myself doing a quick comparison to a melt close toit in this ∆4 firing. As expected, it was an unfused dry powder whichcrumbled apart when poked at.

• Test B, 5 parts Bone Ash with 1 part Alberta Slip and 1 part Frit3110, is a hard white fused mass with deep cracks. Without AlbertaSlip would this make a nice ∆4 sculptural glaze like the Sperry MudCrack?

• For Test C, there’s 4 parts Bone Ash with 2 parts Alberta Slip and Frit

3110, there’s more shrink, and a little bit of coloration from the iron inthe Alberta.

• Test D contains equal parts Bone Ash and Alberta slip with a little Frit3110 included in proportions (3:3:1). This produced a nice colorationbut the texture is rough, indicating incomplete melting. But on theedge, there’s a nice hint of red like an Ohata Kaki glaze. This is oneI’m looking for and want to develop.

• Test E is a combination of 2 parts Bone Ash and 4 parts Alberta Slipwith 1 part Frit 3110. It has the appearance of a nice sculptural glaze,

but the color is brown with a light tone of green. Just as it appears.

• Test F actually looks like it fluxed over. There’s 1 part Bone Ash, 5parts Alberta Slip, and 1 part Frit 3110. Also, just like it looks, thoughthere’s an appearance of cracks under the top surface layer.

Other Questions.

With this line blend, the middle test, Test D, shows a dark maroon colorthough with a rough texture, indicating an incomplete melt and under-firing.This gives me distinct hope that an iron red can be developed for ∆4 neutral

firing. I’m attempting a triaxial blend based on these three ingredients witha small bit of Talc included since Magnesium appears to promote the redcoloration in ∆10 glazes.

Another comment which is important to note with this line blend is thatthere appears to be a little fuming going on with the bone ash. That is,

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there is an area surrounding each test where the bare clay appears to have

a deposit which interacted with it; this diameter appears to diminish withrespect to the proportional amount of bone ash present in the test. Is thisfuming from the phosphorous being released? Or a separate component inthe Bone Ash? Is there a loss of mass of the Bone Ash due to sublimation?

Frit 3195 and Silica.

Listed as“Test Letter”,(Frit 3195, Silica)

A,(5,1) B,(4,2) C,(3,3) D,(2,4) E,(1,5)

Comments and Notes.

Apparently this series of Frit 3195 and Silica is pretty benign. There doesn’tappear to be any benefit of adding Silica to Frit 3195 at ∆4.

• Test A contains 5 parts Frit 3195 and 1 part Silica. This blend didfuse and had both a blue coloration showing in the mix and many finebubbles in it.

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• Test B is a blend of 4 parts Frit 3195 and 2 parts Silica with a nice

white almost satin appearance. There are a bunch of bubbles in themelt. And it just appears that the blend is on the verge of meltingcompletely.

• This blend, Test C, of 3 parts Frit 3195 and 3 parts Silica, but thereis definitely incomplete melting and a surface which wrinkles. Wouldthis incomplete melting and wrinkling still occur with Iron Oxide inthe mix or some other metal oxide?

• Test D, of 2 parts Frit 3195 and 4 parts Silica has not melted muchat all. The frit melted, but did not provide enough melted volume tomake the silica soluble.

• Test E, 1 part Frit 3195 and 5 parts Silica is just a button of Silicabound in a frit matrix. It’s fused solid enough to be removed as asingle button, but not melted completely.

Other Questions.

Just simply not enough solvent (melt) for nearly all these tests.

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Gerstley Borate and Frit 3124 with Alberta Slip.

Listed as“Test Letter”,(Gerstley Borate, Frit 3124, Alberta Slip)

A,(5,1,3) B,(4,2,3) C,(3,3,3) D,(2,4,3) E,(1,5,3)

Comments and Notes.

• Test A with a blend of 5 parts Gerstley Borate, 1 part Frit 3124, and3 parts Alberta Slip shows to be a nice dark greenish clear.

• In Test B, 4 parts Gerstley Borate, 2 parts Frit 3124, and 3 partsAlberta Slip, a hint of milkiness comes in. Also, the crazing appearsreduced.

• Test C, equal parts by volume of Gerstley Borate, Frit 3124, and Al-

berta Slip shows light crazing and more milkiness.

• Test D shows no crazing and a heavier milkiness with a more pro-nounced blueing, from a blend of 2 parts Gerstley Borate, 4 parts Frit3124, and 3 parts Alberta Slip.

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• For Test E, the blend is 1 part Gerstley Borate and 5 parts Frit 3124,

but the appearance is as if there were little Alberta slip in it. I supposedthis might be true due to incomplete mixing in the plastic cup, butlooking closer, I think it has more to do with the fact that in the ceramictest cup, there is only a thin layer of glaze at all, with no appearanceof crazing. This leads me to think that the mix was correct, just thin.

Other Questions.

While these are all very similar in appearance, the practicality of use forthese glazes is dependent on the tuning of the glaze to have proper fit to theclay body. Though the more Frit 3124, the better in appearance is the fit,

i.e. no crazing.

5 Examples of Phase Diagrams for Ideas

Here I mention again the awesome resource which I found on the web forfinding eutectics usable in general ceramics work. The website and databaseis: www.sgte.org/fact/documentation.

Some examples I have found include:

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This one is most applicable to a line blend of Whiting and Red Iron

Oxide. Whiting decomposes at 848◦

C from Calcium Carbonate to CalciumOxide (CaO) in the diagram and Red Iron Oxide is simply Fe2O3; so forfiring above Orton cone 012, this phase diagram is applicable. Looking atthe diagram, we can see that there is a liquid state for this mix at a mole ratioof Fe2O3

CaO+Fe2O3

≈ .58 at a temperature of ≈ 1225◦C. Since this temperature isa little high with regards to the temperature we are trying to fire to, it mightbe of use to try a line blend for this ratio with some fluxing agent, or solventlike Frit 3194. If I try this I will convert the mole ratio for the CaO toan equivalent weight of Whiting, find the correct weight for the Iron Oxide,blend these two, then make a line blend of this mix with the frit, or GerstleyBorate for example.

Another example is the Aluminum Oxide-Manganese Oxide-Silica eutec-tic. My understanding is that the shaded grey areas in the triaxial blendshown are the liquid phases for this blend. So we can see a range of areaswhere we might have a successful glaze at ∆4.

Note that below is the phase diagram for the eutectic for Calcium Oxide,Silica, and Aluminum Oxide listed in section 2, but only at a temperatureof 1200◦C. It is a reasonable guess that fixing a point on this diagram formole ratios, then adding additional ingredients would likely have the effect

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of intensifying the melting of the mix, as shown above with the addition of

Yellow Ochre (hydrated Iron Oxide) to the eutectic base glaze.

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rctc cone 4 initial tests

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