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Macro-Crystalline Zinc Glaze - Combining With A Clear All-Over Glaze?

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oly    13

Been inspired to attempt to combine areas of macro-crystalline glaze effect with my slip-illustrated/sgraffito work. I know this sounds a potential hotch-potch but I have a clear idea in my mind how it will look and I just need to find out how to make it happen....

 

I'm assuming if I was to lay down a small area or patch of macro-crystalline glaze on a flat tile or the inside of shallow bowl and then layer it with a regular clear glaze, the crystalline glaze will be messed up by the ingredients in the clear glaze. 

 

Perhaps I could lay down a patch of crystalline, then mask it before dipping in the clear glaze, so only the edges would merge – could get messy.

 

Obviously it all become more complicated on a vertical surface where the glazed would flow, which I will have to tackle if the tiles worked out.

 

Very grateful for any advice / words of wisdom... :)

 

 

PS. I have a Michael Bailey recipe which at the moment is the one I'm thinking to try working with...

 

Frit 3110        75% weight 

Zinc Oxide     25% weight

 

Suggests various oxides for colour such as...  Copper Carb 2 and Tin Ox 5

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oly    13

Let me think about this for a bit Oly.  Some chemistry you will have to overcome.

 

Thanks – 'chemistry' sounds ominous - remember I am only really an illustrator playing with clay.

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Marcia Selsor    1,301

The tough part of crystalline glazes is that they must be very fluid to form crystals and the  location is fairly random unless seeding. I am sure Nerd will have much to contribute. 

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glazenerd    816

Oly:

 

First, you have to realize how fluid crystalline glaze is: very! If you apply it to the top half, it will run almost to the bottom. As Marcia points out, it has to be fluid in order to form crystals. Secondly, crystalline glaze requires extended hold periods in order to form: 2-6 hours of ramp holds. This will effect any regular glaze you have. It will matte out any clear gloss or satin, and iron in other glazes will crystallize as well.

Lastly; the recipe you show will not grow crystals ( in the standard form anyway). Crystals are Zno(4) Sio4 meaning there has to be nearly equal feed stock of zinc and silica in order for them to grow. The "starter" recipe is 50% frit 3110, 25% zinc! and 25% silica. Zinc is adjusted up or down to control crystal growth, and silica is adjusted to control grazing. At cone 6, 4% lithium carb. Is also required, as is titanium as a seeding agent.

 

Everything effects crystalline glaze: and I do mean everything. Crystals work best on porcelain, although a limited amount of stoneware will grow them pending formulation. Be forewarned: crystalline glaze is a very deep rabbit hole: which is why only 1 in 1000 potters even attempt them.

 

Nerd

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oly    13

Oly:

 

First, you have to realize how fluid crystalline glaze is: very! If you apply it to the top half, it will run almost to the bottom. As Marcia points out, it has to be fluid in order to form crystals. Secondly, crystalline glaze requires extended hold periods in order to form: 2-6 hours of ramp holds. This will effect any regular glaze you have. It will matte out any clear gloss or satin, and iron in other glazes will crystallize as well.

Lastly; the recipe you show will not grow crystals ( in the standard form anyway). Crystals are Zno(4) Sio4 meaning there has to be nearly equal feed stock of zinc and silica in order for them to grow. The "starter" recipe is 50% frit 3110, 25% zinc! and 25% silica. Zinc is adjusted up or down to control crystal growth, and silica is adjusted to control grazing. At cone 6, 4% lithium carb. Is also required, as is titanium as a seeding agent.

 

Everything effects crystalline glaze: and I do mean everything. Crystals work best on porcelain, although a limited amount of stoneware will grow them pending formulation. Be forewarned: crystalline glaze is a very deep rabbit hole: which is why only 1 in 1000 potters even attempt them.

 

Nerd

 

Thanks very much for the reply – that gives a lot of food for thought

 

The greatest problems seems to be....

 

a) keeping a clear glaze alongside crystal growth – maybe if I had a real hire-fire clear glaze that could cope with the extended cooling period if I was only firing to cone 6 (with lithium carb if required)?

 

B) glaze running off pot – this could be insurmountable – perhaps I could only use the effect on insides of shallow bowls?

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glazenerd    816

4% lithium is for cone 6. Cone 10 needs under 1% pending frit of choice. You can add 1% alumina to hinder glaze run, but it will have some effect on development: acceptable in your case. Even still, you could only do the top half of the piece. Inside of a bowl: do as you wish: no place for the glaze to run off.

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oly    13

4% lithium is for cone 6. Cone 10 needs under 1% pending frit of choice. You can add 1% alumina to hinder glaze run, but it will have some effect on development: acceptable in your case. Even still, you could only do the top half of the piece. Inside of a bowl: do as you wish: no place for the glaze to run off.

 

Very many thanks, can you possibly tell me, is the "starter" recipe of 50% frit 3110, 25% zinc! and 25% silica likely to be a clear glaze when fired unseeded?

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glazenerd    816

Yes, it is a clear glaze, with very high opacity. Seeding would produce white crystals. Which brings me to the final issue: crystalline glaze has a COE in the high 8' s. So you would have to formulate other glazes in that general range.

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I had a relay fail on a kiln, half the elements fused on for an extra 12 hours. Clear glaze came out looking fine. I think you could find a clear that holds up to crystal firing times. Not that I have ever tried a crystal glaze/firing.

 

Layering a clear over doesn't sound possible but masking could work.

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oly    13

Thanks very much for the replies, I'm slowly getting my head around what might be involved....  :wacko:

 

With regard to oxides to get different colour crystals I've got cobalt and copper, and also some red iron, but thinking to get a nice bright red or orange crystal can anyone give a hint as to best oxides to start experimenting with, to put me on right track? A purple/mauve would be nice too ;)

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glazenerd    816

Oly:

What you do not what to do is over- saturate with oxides: some exceptions. Cobalt for instance requires only 0.25% of total recipe weight to produce medium blue. Iron ox you can go from 1-5% to get amber to deeper hues. Copper carb., start with 0.50% to get a light green.

 

I have an orange out there, trying to remember: high rutile 10-12%, and low....hmmm. Will have to go out and look. Just remember that oxides work and act differently in crystalline.

 

Nerd

 

Forgot something: red is done by reducing copper. Purples are done with high titanium, mostly sourced through ilemnite. Also, titanium is considered a colorant as well in higher %.

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Dick White    154

The priority of colors of the crystals is based on the electron valence of the metal oxide colorant(s) in the recipe. The colorant with a higher priority will go to the crystal first and the lower priorities will stay in the background. E.g., cobalt has the highest priority and will always be the crystal color, while copper has the lowest priority and will always stay in the ground if there is another oxide present. Thus, there will never be green crystals on blue ground, only blue on green.

 

The molecular crystalline matrix absorbs the metal oxide colorants as it develops, so using a stain to color the crystal is not viable. Further, the crystalline glaze recipe is so caustic that any conventional stain in the glaze will be broken down into its constituent oxides and the colors will move to the crystal or ground according to their respective priorities. The only stains that will resist the caustic glaze are zirconium encapsulated inclusion stains. These are, for the most part, in the red and orange hues owing to the cadmium and selenium content. Other colors made with the usual suspects do not need to be encapsulated and so the stain companies don't bother making those as inclusion stains. However, because the crystal color is dependent on incorporating the oxide into the developing matrix, these inclusion stains will not go to the crystal, but stay in the background. The most effective way to use the red or orange stains as a background for crystalline work is to put the stain in a vitreous engobe that is applied to the bisqued form and fired again to fuse the engobe to the substrate, and then apply an uncolored crystalline glaze to create white crystals on the red/orange ground.

 

The above notes relate to oxidation firing. If you have sufficient control over a reduction firing, a completely different world of color is available, just as with the same oxides in conventional glazes.

 

Welcome to the rabbit hole. Nerd is your best tour guide down here.

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glazenerd    816

Dick:

I was not going to overwhelm Oly with information until he waded out far enough to realize he is sinking fast in quicksand. Rofl

 

Isoelectric band gap chart. The weaker values will be over powered by the stronger values.

 

Compound Periodic Name Isoelectric Value Melting Point

Tungsten Oxide WO(3) 0.2-0.5

Antimony Oxide Sb(2)O(5) 0.4-1.9

Vandium Oxide V(2)O(5) 1.2-3

Silica Dioxide SiO(2) 1.7-3.5 3025F

Tin Oxide SnO(2) 4.5-5.7

Mangenese (Di)Oxide MnO(2) 4.1-5.0

Titanium Dioxide TiO(2) 3.9-8.2*

Rutile TiO(2)* 3.9-8.3

Iron Oxide Fe(3)O(4)** 6.5-6.8 2850F

Iron Oxide (alpha) Fe(2)O(3)*** 8.4-8.6 2850F

Chromium Oxide Cr(2)O(3) 6.2-8.1

Alumina Oxide Al(2)O(3) 8.1-9

Copper Oxide CuO 9.5-9.6

Zinc Oxide ZnO 8.7-10.3 3587F

 

My personal reduction potential/ isoelectric point chart.. feel free to cut and paste it ...from UC-Berkley

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Dick White    154

Yes, rofl. In my observations in the pottery world, one must stay as far away as possible from the entrance to the rabbit hole, as once near it the siren call will suck you in and then you can't get out.

 

And an easier (haha) purple is 1/2% Mn and <0.05% Co... i.e., wave the bag of Co over the glaze mix and maybe just enough will fall off your dirty fingers.

 

And further to Nerd's list of oxides - in the crystalline world, do not even think of chromium for whatever colors it might create elsewhere. Crystalline glazes are very high in zinc. The color of chromium in the presence of zinc is (you know what) brown. Don't. Just Don't. And further to that thought, don't use any stain that has Cr as a component. E.g., all the black Mason stains have Cr as a component oxide, which for us means sh** brown is the new black.

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oly    13

Thanks so much everyone for all this great advice I will try to post any interesting results in due course :)

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Marcia Selsor    1,301

Glazenerd, where is the nickel in your list? That was my all time favorite colorant in Crystalline glazes. I also had tungsten, molybdenum, uranium nitrate gifted to me from the Chemistry dept.

Marcia

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glazenerd    816

Marcia:

The complete list is on my laptop that CRASHED! This fall, I am taking up to a local guy to fish my research files out of it. I do recall that cobalt, nickel and moly were at the top of the list near zinc. If you notice, zinc is on the top and silica on the bottom: the strongest and weakest forming ionic bonds.

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oly    13

Oly:

 

First, you have to realize how fluid crystalline glaze is: very! If you apply it to the top half, it will run almost to the bottom. As Marcia points out, it has to be fluid in order to form crystals. Secondly, crystalline glaze requires extended hold periods in order to form: 2-6 hours of ramp holds. This will effect any regular glaze you have. It will matte out any clear gloss or satin, and iron in other glazes will crystallize as well.

Lastly; the recipe you show will not grow crystals ( in the standard form anyway). Crystals are Zno(4) Sio4 meaning there has to be nearly equal feed stock of zinc and silica in order for them to grow. The "starter" recipe is 50% frit 3110, 25% zinc! and 25% silica. Zinc is adjusted up or down to control crystal growth, and silica is adjusted to control grazing. At cone 6, 4% lithium carb. Is also required, as is titanium as a seeding agent.

 

Everything effects crystalline glaze: and I do mean everything. Crystals work best on porcelain, although a limited amount of stoneware will grow them pending formulation. Be forewarned: crystalline glaze is a very deep rabbit hole: which is why only 1 in 1000 potters even attempt them.

 

Nerd

 

 

Hi GlazeNerd

 

I'm just looking at this again as I make preparations to experiment. One question, that Michael Bailey recipe for crystal growth...

 

Frit 3110        75% weight 

Zinc Oxide     25% weight

 

Would the Frit not contain enough Silica for crystal growth, I ask because it is listed as 69.77% SiO2?

 

Sorry, I am now reading your recent post on crystal growth so suspect the answers are all in there!

Edited by oly

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glazenerd    816

Oly:

Have seen this recipe before, and the end intent is to grow a smaller population of small crystals. One caution, with 75% frit you will have a river flowing off the pot if you over flux. Does the recipe call for lithium carb., if not then it is designed for cone 10. To use at cone 6, add 2 % lithium carb. To start. Have to be abundantly cautious with lithium.

Nerd

 

Edit: first line corrected to read: smaller population.

Edited by glazenerd

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Dick White    154

FWIW, this recipe was promulgated by Michael Bailey in his book "Glazes Cone 6," on page 52.The published recipe (just 75% 3110 & 25% ZnO) included 2% CuCO3 and 5% SnO. The accompanying text reads: "One interesting characteristic of [this glaze] is that, in combination with tin oxide and copper carbonate, it can even form crystals without the need for a special cooling cycle. This was discovered by accident when the kiln controller failed to run the cooling part of the program. This could be useful in, say, a teaching situation, where one might like to demonstrate a crystal growing glaze with having to change the normal type of firing (taking the kiln up to temperature and switching off)." The pictures on the same page show other tiles with several different oxide colorant combinations, each soaked for 4 hours at temps of 950C - 1100C.

 

The book offers a second recipe of 50% 3110 / 25% ZnO / 25% SiO2. This is a more conventional gathering, but as Nerd points out, typically would have some LiCO3 for cone 6. This book is, by its own title, only cone 6 work, so I don't understand the absence of the Li in the recipe in the publication. But what do I know?

 

I tried the first recipe once (with no downfiring) just for S&G on the inside of a bowl as I had no idea what would happen and I didn't want to go the usual extremes with catcher saucers and risers. Meh. It was a very pretty aqua turquoise green (as would be expected with a very high alkaline copper/tin glaze) but the crystals were underwhelming. Or maybe I just did it wrong. Wouldn't be the first time.

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glazenerd    816

DW:

As with all things crystalline: any basic crystalline recipe will achieve micro formations if the cooling period from 2000-1800F is slow enough due to kiln size, packing density: IE> thermal mass. As Oly pointed out: 62.00 +/- molar silica is proportionate to a 20% silica addition. My Nerd O' meter thinks if you used this recipe as a base for a thicker growing medium at optimal flow: and added 10% silica and incorporated the usual holds: you very well may end up with mega crystals.. Hmmm... crystalline experiment # 2489.

 

 

but the crystals were underwhelming. Or maybe I just did it wrong.

You did it right, some potters like the look of micro crystals.

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Tyler Miller    331

Tom's hit on a variable most don't think about--thermal mass. Underwhelming crystals from a regular cooling cycle would benefit from a large, fully packed. extra insulated kiln. There's still a devit window at work, and crystal growth still a function of time within that window. How big is Michael Bailey's kiln?

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oly    13

Oly:

Have seen this recipe before, and the end intent is to grow a smaller population of small crystals. One caution, with 75% frit you will have a river flowing off the pot if you over flux. Does the recipe call for lithium carb., if not then it is designed for cone 10. To use at cone 6, add 2 % lithium carb. To start. Have to be abundantly cautious with lithium.

Nerd

 

Edit: first line corrected to read: smaller population.

Interestingly the author proposes it as a cone 6 recipe and suggests 3 different 4-hour cooling periods to get different crystal growth. No lithium involved though.

Edited by oly

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glazenerd    816

Oly:

Frit 3110 has a melt range in the 1500-1600f range, if memory serves. So it is feasible that no lithium additions were made pending his upper end firing cycle. The fluidity of the glaze is the most paramount issue: rather you achieve that through heat, or less heat plus flux. Going to add some critical firing information and crystal formation criteria to my crystalline thread this weekend. If you are going to fire crystalline, then you have to learn how to read crystals. The structures and formations will tell you how much more/ less heat you need. It is one of those "secrets" DW was talking about, that you will not find in books.

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