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Joseph

Your Variations On Leach Clear

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I have been using the variants of leach clear that appear in the John Britt high fire glaze book. This is the base recipe

 

40 Custer Feldspar 
30 Silica or Flint 
20 whiting 
10 EPK Kaolin 

 

Does anyone have recipes using this base they would like to share. The book includes a white using zircopax, a green with iron and a temmoku. I have been thinking of subbing yellow ocher for the EPK.

 

thanks in advance for sharing 

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You might not want to remove the kaolin. This gaze can settle out pretty hard due to the amount and type of clay content. I usually add some white firing bentonite and epsom salt to help keep it from hard panning.

 

In addition, the clay content is keeping the glaze from being too runny at temp. Without the clay it might run off the pot onto the kiln shelves.

 

The ochre might act as a flux making the glaze more fluid on top of that.

 

Try a line blend adding the ochre.

 

Another couple of oxides i have enjoyed playing with are combinations of rutile or titanium and iron.

 

I did a whole series of tests with each in varying amounts from 0%-8%.

 

My favorites were the 2-4% range.

 

Mix a big batch with no colorants Split this into three containers.

Add 8% iron to one and 8% rutile to the other and do volume measured blends.

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joseph, i have been looking for a cone 6 clear that will not make a green underglaze turn grey.  this recipe does not have a cone # and the definition of "high fire" is sometimes only ^10 and other times includes ^6.  i also single fire in an electric kiln and spray glazes.  do you know if this will work at cone 6?

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I've done se recent experimentation with the 4/3/2/1 recipes. I've fired these at cone 8 with 3 hour hold time. Trying to get as close to possible to what I plan on doing with a possible upcoming anagama kiln. Some tweaking is bound to be needed for that. Here are my results and feel free to look around for other info on the blog. https://dreamsofearth.wordpress.com/2015/04/30/testing-results/

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Oh I forgot to mention that the clear didn't turn out as expected. Maybe not mixed thoroughly or was in a cold spot in the kiln. It turned out opaque and looked under fired. Which is weird since all the other recipes are the basis of this. Logic says it should have melted. But I don't trust my kiln as far as I can throw it.

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Hi Joseph,

My former firing partner, Gary Zeiner, did a series of tests of what we called "1-2-3-4" in ^10 reduction on porcelain and red stoneware.

He found that all benefited from an addition of 2% Bone Ash. Here are the most promising:

 

Creamy yellow on stoneware - add 3% rutile, 2% copper, 2% bone ash

Light green on both - 2% iron, 2% bone ash

Red on both - 2% copper, 2% bone ash, a pinch of cobalt (less than 1/2% - this is to prevent snot green when it doesn't reduce to red, I think Tom Coleman does this, too)

Light brown on stoneware - 5% manganese, 5% titanium, 2% bone ash

Green blue on stoneware - 3% rutile, 3% red iron oxide, 2% bone ash

 

OldLady:

according to an old Axner Mason Stain handout, chrome greens will go brownish unless there is 12-15% whiting in the over glaze as well as No zinc. Hard to find at this range, but, if the Leach doesn't work out, you might try James Chappell's (Clay and Glazes) clear satin mat ^1-6 (WFG-8):

Whiting. 18.3

Lithium carb 4.1

Pemco#54. 12.2

Kaolin. 12.2

Calcined kaolin. 12.2

Silica. 41

 

I would try adding some copper to your green UG, maybe a pinch cobalt, too, and make your own custom UG.

Rae

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In my experience this is a cone 9-10 glaze. If you have a 3 hour hold at cone 8, you're pushing it to cone ten with heat work. It is sensitive to colourants, changes in ingredients, and to reduction atmosphere. The clay body underneath it will affect how it looks as well. The whiter the clay, the bluer it goes in reduction. (See that front bowl in my avatar.). That one has a small amount of ochre and a touch of tin (don't have the recipe in front of me, but it's nowhere near 10%.) it's fired in a gas reduction to cone ten and it's on a porcelaineous stoneware body. (Plainsman h570).

I use EPK in mine, and Custer for the feldspar. It only hard pans for me when it's been frozen, but I mix the bucket at least once a month. It shows every application drip. It crazes on my clay.

 

I would not suggest removing the EPK, but you can certainly use other iron bearing clays as colourants. Try Alberta Slip for a tenmoku, maybe? And the iron/rutile combo is worth pursuing, but it can make an otherwise stable glaze run in rather surprising ways. Make sure you factor for this in your testing. (I don't have an example to hand to photograph, but I've used it.)

 

Synj00, It is a good liner glaze for a wood kiln.

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If you're not married to the Leach, Zeiner made me a clear that doesn't craze. Try with the same % of colorants:

GZ Clear

60 Silica

60 Custer

40 Whiting

40 Ball

 

Synj00: The bone ash is a flux that helps with Leach's crazing

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thank you, rae, so, no cone 6 clear.  except the few i have used, some of which do leave the green alone, i will check for percentage of whiting.  i have a great cone 6 matte and a nice satin.  it is a Kathy Triplett satin matte and has no zinc and 15% whiting.  i do not fire often but will make sure i do a green test next firing.

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thank you, rae, so, no cone 6 clear.  except the few i have used, some of which do leave the green alone, i will check for percentage of whiting.  i have a great cone 6 matte and a nice satin.  it is a Kathy Triplett satin matte and has no zinc and 15% whiting.  i do not fire often but will make sure i do a green test next firing.

Chappell says you can make a semi-gloss more glossy by

A. Increase flux by 1-2% (frit, Ger Bor, talc, lithium carb, spodumene or lead bisilicate)

B. Decrease refractory element by the same amount (kaolin, whiting, wollastonite, clay content or silica)

It might take several tests/adjustments.

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Bone ash or tricalcium phosphate in this small quantity will keep the glaze from settling out in the bucket, and it can cause it to gel. If it gels, it's tempting to add more water, which makes for a thinner glaze layer. It's easier to add a bit of deflocculant to solve any settling problems. Bone ash supplies calcium, which is already present in the calcium carb. It doesn't prevent crazing. Check the glaze on your clay body to see if it crazes before trying to doctor it. How to solve crazing depends on the difference between the coefficient of expansion of your glaze, and that of the glaze.

 

http://digitalfire.com/4sight/material/bone_ash_123.html

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What benefit does the bone ash play? I've seen a lot of variations using Epsom salt as well. Is that to keep it from solidifying?

The bone ash is a calcium phosphate. It causes a better glaze melt. Epsom Salts is just in there to prevent the glaze from settling.

TJR.

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I have been using the variants of leach clear that appear in the John Britt high fire glaze book. This is the base recipe

 

40 Custer Feldspar 

30 Silica or Flint 

20 whiting 

10 EPK Kaolin 

 

Does anyone have recipes using this base they would like to share. The book includes a white using zircopax, a green with iron and a temmoku. I have been thinking of subbing yellow ocher for the EPK.

 

thanks in advance for sharing 

Keep the EPK in. Sub the yellow ochre for iron oxide in the celadon.

TJR.

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I have been using the variants of leach clear that appear in the John Britt high fire glaze book. This is the base recipe

 

40 Custer Feldspar 

30 Silica or Flint 

20 whiting 

10 EPK Kaolin 

 

Does anyone have recipes using this base they would like to share. The book includes a white using zircopax, a green with iron and a temmoku. I have been thinking of subbing yellow ocher for the EPK.

 

thanks in advance for sharing 

This glaze would be a good glaze to try doing a Currie blend on.

David

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I would opine that bone ash, though it contains a lot of calcium, is rarely if ever used solely to supply calcium, which can be gotten from whiting with fewer potential difficulties.  It's primarily used to supply phosphorus.  For example, it's an ingredient in every kaki glaze I've seen, and it's added to influence the color development.  It's often an ingredient in chun glazes for its ability to promote colloidal opacity ( though there is much debate in scientific circles about the validity of this idea.)  It can promote a kind of opalescence in some glazes, and a soft mottling effect.

 

I would think it would promote crazing rather than preventing it, since phosphorus oxide has a high CoE.

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Leach celadon is a cone 10 glaze. It reacts with soda to do all kinds of things, depending on the thickness of the soda spray and how it's applied. It was one of my go-to liner glazes when I was doing a lot of soda firing, but I always used it with a colourant. It formed crystals, though, which makes me think there will be some sort of opacification effect.

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