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GreyBird

Hudson River Clay

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1 minute ago, glazenerd said:

Mary:

not so sure this is a straight forward glaze issue. This clay has over 17% total fluxes (molar). In addition, the SiAl ratio is 5.06 - which is off enough to weaken the body.  

T

I've used it here in a glaze recipe over a stoneware cone 6 clay body. So I guess I'm not sure what you are saying? But I guess that's why I am taking the Glaze course which covers clay bodies as well.

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Mary, could you post your original Old Gold Albany recipe that you are subbing Hudson clay in? As adding just 5% feldspar isn't enough I would try a progression blend, adding 5 grams at a time and going up to 25grams per 100 base. Try banging the edges of the un-shivered test tiles against something hard, might see more shivering. Shivering can happen straight away or years later, don't trust a glaze that shivers.

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Sure, 

Old Gold Albany:

Albany Slip:      78%

Lithium Carb: 10%

Zircopax:           12%

No, I don't trust it at all. That is why I am trying to adjust it to be a trustworthy stable glaze :)

Edited by GreyBird

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I'll try that.  :) If I just drop the Lithium Carb the recipe won't add up to 100% does that matter? If it works I guess I would just adjust it to add up to 100% and go with that?

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Mary:

your recipe is 78% clay, 10% strong flux to melt the 78% clay, and 12% colorant to change the color of the 78% clay. So it still comes back to the clay; so I will break it down :

Albany: total fluxes 16.97%. Alumina. 10.51%.  Iron 2.11%   Silica  70.40%.  ( molar %)

Hudson:total fluxes 13.41%  Alumina. 13.52%.  Iron 3.71%. Silica. 68.54%.  (Molar %)

So in formulating: Albany has more total fluxes, so it needs less flux additions to melt- Hudson needs more. Hudson has a third more alumina and less silica than Albany which throws off the SiAl ratio. Did you notice in the recipe Min posted: the 5% alumina hydrate addition? That was done to balance the SiAl ratio, to bring it into limits. Alumina adds strength to clay, just as it does glaze. Finally, Albany has 2.11% iron and Hudson 3.71%. When firing to cone six: iron has to be factored in as additional flux. It is this same iron level variation playing into the color: with some minor contributions elsewhere. 

I would shy away from any sodium additions due to the clay content of the recipe: pin hole issues are probable. Potassium would be a good alternate choice. Hudson already has a high calcium content: no need to add that either. Montmorillonite based clays are very plastic, but also very weak. In your case, prone to shivering. You could also use your original recipe and add 5% alumina hydrate to that. Another variation: add 10% EPK ( kaolin is 37% alumina). 

The primary distinction being: you are melting a recipe with 78% clay content. 

T

forgot something: the high level of iron in Hudson could also be playing a role in this problem. High iron content in clay can make it brittle. 

Edited by glazenerd
Forgot something

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Glazenerd, Thank you so much for taking the time to go into this so thoroughly. I feel rather inadequate when it comes to chemistry but I am hoping the glaze class will give me a bit of a boost! 

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OK, I am going to mix these two up tomorrow and see how it goes :)

New Old Gold Albany:
Albany Slip - 75
Frit 3195 - 20
Alumina Hydrate - 5
Tin ox - 4

New Old Gold Hudson:
Hudson Clay - 75
Frit 3195 - 15
EPK - 15
Tin ox - 4

The original had 12% Zircopax. Is there a reason to switch to tin and to lower it to 4%? I really liked the original "Old Gold" Color. I guess I could always try it both ways.

I also found these in "Ceramic Glazemaking" by Richard Behrens. I'll try them as is before making adjustments for shivering :)

Bright Matt Albany:
Lithium Carb 00.9
Zinc ox 09.8
Kaolin 05.2
Albany Slip 84.1

Bright Mottled Albany:
Lithium Carb 14.8
Albany Slip 74.2
Kaolin 11.0
Bentonite 02.0

Edited by GreyBird
Found more info.

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Mary:

Want to see your clay up close?

You can see the alkali film bleeding across the sedimentation lines in the first pic. In the second pic which is towards the surface: looks like the high iron content is oxidizing. You definitely have a large amount of mica: can see the crystals in other views. Which explains the high potassium and higher alumina levels. I did an "unofficial" sieve test yesterday: I sieved about 1/4 pound through a 100 mesh screen. Then I took one level teaspoon and sieved through a 200 mesh screen: about 70% passed. Unofficial, but gives me some indication of what you are dealing with. I can also see a green cast in some views: usually associated with chlorite minerals. Early in the game at this point: but I am going with some smectite variety, which has heavy mica deposits, hematite, and ??? (will have to test more). What I was wrong about: little to no humus.

1645359455_HudsonClay.jpg.824da05906f79152737c40d6e0300989.jpg

Been awhile since I have seen natural clay bleed fluxes.

Hudson2.jpg.65f6678a00ad13ca831a1d930a05b990.jpg

Suspect this is your iron (8.31%) oxidizing as it is exposed to air.

Tom

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WOW, Cool Pics. So interesting. Thanks for sharing though without your narration I wouldn't have a clue as to what I was looking at. LOL. I know that someone else who had done some experimental firing with it had said he had an issue with salt migrating to the surface. Could that be salt in the top pic?

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Both potassium and sodium are naturally occurring salts. In both cases, they can contain 14-20% soluble salts; which indeed migrate. Still makes me wonder if a water treatment plant is dumping upstream? Very unusual. Maybe you should call it "Calgon Hudson Clay" :)

Tom

Will have a test fire out later today: will post later.

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Cone 6. 60% Hudson, 20% spodumene, 20% mahavir potash, 3% NS suspender, 3% lithium. Carb.

so far so good: going to thermal shock when I get time. Just slightly immature, but close. I see red streaks sprinkled throughout. Going to try 50%, which should go red! then 70%. The recipe brings silica just over limits, but the alumina is way heavy ( intentionally). 

image.jpg.ae7f97444d229c47fc4d0314341ff629.jpg

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Mary:

been doing some research, trying to figure out your clay.

calcium bentonite is found in your area. Calcite is mined and abundant all over NY state. More interesting, smecite is fairly common in the Arirondack Mts. Even more interesting is how it is formed: humus is drawn into existing illite deposits on the forest floor and is converted over (much) time to a smecite variety. Even more interesting, native NY smecite has a green/ gray cast: which I saw in your samples. The specific native NY smecite is 0.5 um particle size: in pottery speak 2500 mesh plus. 

Question: how far away is Cherry Hills? And it's proximity to the Hudson? 

Tom

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Thanks so much for sharing all of this info. Quick question. What do you think contributes to the high iron levels? I ask because I believe that area of the Hudson was once a site of great oyster beds. I used to do some oyster work to help spawn oyster beds and I know oysters have a high iron content. Just wondering if anyone is aware if there is a correlation. 

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Gred:

oyster shells would provide calcium, not sure what else?  The iron and magnesium levels are the highest I have seen in natural clays: not sure  what the contributing factors are, but working on it. I originally thought the iron was hematite due to the color, but from reading; magnetite is more common in NY. Later this year I will demineralization a sample and have a look. I am fairly confident it is a combination of calcium bentonite and smecite montrollites. The old Albany slip was classed as non-plastic; this sample is highly plastic- approaching macaloid in nature. Interesting indeed! 

Tom

edit: I will look into the iron levels in oysters

Edited by glazenerd
Info added

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