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I was wondering what the current thinking was on the Val Cushing approach to glaze making of having a base glaze of a certain type and then using oxides for coloring?

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If you have a stable glaze to start with, you can go about making changes methodically in all your materials, not just the colourants. It’s a very good method to learn how different materials affect your glaze. And once you start altering fluxes and other things, you change the nature and the look of your glaze. If you’re starting with a stable base, you aren’t falling in love with glazes that are hopelessly broken and will never fit, or be constantly finicky. 

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I just got my copy of the Handbook and also some handouts that were available on a website as an adjunct to the Handbook. Pretty humbling...what a great man. I like this kind of methodical approach but didn't know what the current thinking was about it. Thanks for the input!

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I have noticed looking on Glazy that glazes appear to have fallen into two groups.....all the cone 6 glazes are oxidation and all the cone 10 glazes are still reduction. I still have some of my cone 10 reduction glazes that used Kingman feldspar and a partial bag of Kingman left. I have not run across many cone 6 reduction glazes. I have been trying to get around to learning Bill's calculation formula for adjusting them to cone 6 but haven't gotten there yet. I don't really want to get a propane service because I think there would be too many questions---and the people around here specialize in being difficult. . So firing the big gas kiln to 6 would be much more manageable . I got an answer from another fellow on the kiln forum that it only took 12 gallons of propane to fire his 2831 Olympic to 6....that just doesn't seem right somehow.  The kiln I built and used in the past had double brick wall soft fire brick. I keep looking at the walls of that 2831 wondering how the thing doesn't start glowing at 10! I am trying out some different bodies for tests as well. I want to settle on one stoneware and one porcelain body.  It's not like I am going to be selling again. I just get to do whatever I want!  Yay! 

Thanks for getting back to me Babs....always a pleasure. 

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It's because most cone 6 people are firing electric kilns, and most cone 10 people fire in gas or wood kilns.  Just because a recipe is marked as oxidation doesn't mean it won't work in reduction, you just have to keep in mind that some colorants will react to a reducing atmosphere and some will not.  Copper is green in oxi, red in reduction, so don't expect a nice copper green in reduction.  Tin and chrome make a beautiful pink to red in oxidation, a tan to pea color in reduction.  Iron is red in oxidation, black in reduction, etc etc.  

You could always just fire your gas kiln to cone 6 in oxidation instead of putting it in reduction and skip all the hullabaloo, but at that point just use an electric kiln and fire for 1/10th the price of propane.

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Size is the issue. The little electric I scarfed up is an Olympic 18 series and only has 18 inch shelves....and then with posts.....it limits me to about a 16 inch piece and you can't have many large pieces unless you have a bunch of small pieces, which I usually don't. . Obviously it also fills up fast.  Then the 2831 gas is humongous--you could fire a three foot high pot in it...but it will take forever to get enough ware to fill it up. Since I probably would only fire it once a year....the propane cost is not so much of an issue for me...as I am not in this anymore  to make money.  I also saw the gentleman who has a new 2831 and was reporting black smoking when he was trying to keep the burners on low....but he also had four burners and had built a make shift firewall with shelves. So he got reduction whether he wanted it or not.  I have the six burner system.  I don't think it's really possible not to have some degree of reduction with gas....so you might as well go  for reduction. 

Thanks for the oxide tips!  Much appreciated!  I never got a copper red in reduction....but I think that was because the glaze formulations back then were so primitive compared to now. Val Cushing had several copper reds and Glazy has many also. I must admit I find the tin and Strontium blues very interesting. It's just such a pleasure to have so many choices now!  Now....if my damn materials ever show up, I can start testing the 6 glazes.  They must be at the end of the trip....they started out in Tacoma and are in Cleveland now.  Do you order from Clay Art Center or from Laguna? I am also doing a "poll" on clay bodies....which ones do you like?  So far I tried that stoneware with grog which I hate, Amaco #38, "Oregon White" cone 6 porcelain from Clay Art Center, New Zealand and White Rose porcelain. I love the feel of the New Zealand but it is a glassy porcelain with all the attendant problems....the White Rose is toothy. I am having the most trouble finding a good white stoneware. The Amaco was "ok" but nothing to write home about. Your input would be appreciated. 

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Copper red in reduction perhaps but linked with right recipe..containing zinc from memory , yes

Memory not infallible these days.

I miss my gas kiln..have I said this before?

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13 minutes ago, Babs said:

Copper red in reduction perhaps but linked with right recipe..containing zinc from memory , yes

Memory not infallible these days.

I miss my gas kiln..have I said this before?

Maybe you're thinking of tin-chrome reds, which require calcium and will bleach out with zinc?

I think copper reds come out best when a full load of copper pottery is fired since it flashes as a vapor and helps to saturate the pots with Cu2O (red iron oxide).  It's one of those things that needs to be dialed in.

This was fired in oxidation and has very little copper (1.75 parts) and it STILL turned slightly red.  Pretty interesting! I believe this is something called peach blossoming

LRM_EXPORT_532726771610767_20190618_101432474-1728x1152.jpeg

Edited by liambesaw

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Most copper reds require tin oxide.

"Sn does a couple things. First it improves the solubility of Cu. Metals, per se, aren't really very soluble in glaze and if you can't get the metal dissolved, it can't very well be precipitated in any organized fashion. Second, on cooling, Cu tends to attract Sn atoms from the glaze. These atoms sort of "coat" the crystals as they are developed and thus serves to control their size by limiting the attachment of further Cu atoms to the crystal. This behavior is that of a protective colloid and it is of great advantage. Because if the crystals get big, the glaze turns "livery" looking, and the doughnut remains elusive. Third, to the extent that Sn has limited solubility in SiO2 or B2O3 based glassy material, it probably also serves to provide nuclei on which the coloring crystals can grow."

A study of the mechanism behind the color in color red glazes by Karl Platt.

Zinc is a bit of a wild card in reduction.

"Zinc-containing glazes may be quite variable and unpredictable in reduction depending on how carefully you duplicate conditions firing to firing and how uniform the interior of your kiln is." John Hesselberth

 

Edited by C.Banks

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7 minutes ago, C.Banks said:

Most copper reds require tin oxide.

"Sn does a couple things. First it improves the solubility of Cu. Metals, per se, aren't really very soluble in glaze and if you can't get the metal dissolved, it can't very well be precipitated in any organized fashion. Second, on cooling, Cu tends to attract Sn atoms from the glaze. These atoms sort of "coat" the crystals as they are developed and thus serves to control their size by limiting the attachment of further Cu atoms to the crystal. This behavior is that of a protective colloid and it is of great advantage. Because if the crystals get big, the glaze turns "livery" looking, and the doughnut remains elusive. Third, to the extent that Sn has limited solubility in SiO2 or B2O3 based glassy material, it probably also serves to provide nuclei on which the coloring crystals can grow."

A study of the mechanism behind the color in color red glazes by Karl Platt.

Zinc is a bit of a wild card in reduction.

"Zinc-containing glazes may be quite variable and unpredictable in reduction depending on how carefully you duplicate conditions firing to firing and how uniform the interior of your kiln is." John Hesselberth

 

And very little tin!

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57 minutes ago, C.Banks said:

Most copper reds require tin oxide.

"Sn does a couple things. First it improves the solubility of Cu. Metals, per se, aren't really very soluble in glaze and if you can't get the metal dissolved, it can't very well be precipitated in any organized fashion. Second, on cooling, Cu tends to attract Sn atoms from the glaze. These atoms sort of "coat" the crystals as they are developed and thus serves to control their size by limiting the attachment of further Cu atoms to the crystal. This behavior is that of a protective colloid and it is of great advantage. Because if the crystals get big, the glaze turns "livery" looking, and the doughnut remains elusive. Third, to the extent that Sn has limited solubility in SiO2 or B2O3 based glassy material, it probably also serves to provide nuclei on which the coloring crystals can grow."

A study of the mechanism behind the color in color red glazes by Karl Platt.

Zinc is a bit of a wild card in reduction.

"Zinc-containing glazes may be quite variable and unpredictable in reduction depending on how carefully you duplicate conditions firing to firing and how uniform the interior of your kiln is." John Hesselberth

 

As above, but with respect to apportionment:

Common copper red recipes for reduction contain  0.25%  to 0 .5% copper and three times more tin. Tin is essential for decent copper red development in reduction. Fluxes are generally sodium and calcium but traces of potassium and magnesium are fine. Many modern recipes contain some boron as generally the glossier the better the appearance of red.

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3 hours ago, liambesaw said:

Maybe you're thinking of tin-chrome reds, which require calcium and will bleach out with zinc?

I think copper reds come out best when a full load of copper pottery is fired since it flashes as a vapor and helps to saturate the pots with Cu2O (red iron oxide).  It's one of those things that needs to be dialed in.

This was fired in oxidation and has very little copper (1.75 parts) and it STILL turned slightly red.  Pretty interesting! I believe this is something called peach blossoming

LRM_EXPORT_532726771610767_20190618_101432474-1728x1152.jpeg

Interesting!!! 

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What were you firing Babs?   One you built or a commercial one? I have this monster 2831 Olympic I have been lugging around for 35 years....never been fired. I have a request into Olympic about propane consumption so I know what size tanks to buy. Mine has six burners instead of the four now. I think the firing will be more even than with the four burners. I am trying to figure out how to reach the bottom! I still have some of my Kingman Glazes...did I say that before? Memory going here too! 

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I was firing an early made fibre kiln.  Zoomed up and crash cooled so had to be listened to.

I just used to put miniscule amount of copper in a majolica glaze  I used both   in oxidation and reduction when firing in the gas kiln so yes the tin was there as well as the zinc. Cone 5/6

How to reach the bottom????

A top loader?

Lovely footage of Lucy Rie head down bottom up into a top loader at age of  about 90

so go for it but have some stabilizer for your legs, a friendly hand on rear or keep up those back strengthening asanas:-))

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you could have someone with longer arms put a shelf into the bottom using posts under it.  make sure you can then reach the new "bottom".   i had to do this recently.

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Yes.... I realized here in the past few days that I am going to have to move the kiln closer to the electrical outlet and also get it closer to the door of the shop so I can open the door to vent it during firing.....so I will set up that bottom shelf when we do that. I was surprised when I looked at the kiln furniture package that came with it that the one thing that was missing was the three inch posts for the first shelf.  So had to order those. Also....these shelves are humongous....glad they are all half shelves. Thank you for getting back to me,

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For a few years I used a 5 section stacking kiln, I am 5'9", I found this was tough for me so I eased it by setting up a pulley in the ceiling with a cable set to a 3 cable split. This allowed me to lift the 5th section then put it down after the section was loaded. Lid stayed on 5 all the time. Takes so effort to set up, but it does work. I never had a vent, so that was not in the way.

 

best,

Pres

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I think that is a little too high tech for me, but thank you for the suggestion. I am hoping the additional four inches from the posts and the shelves will make the difference.  I am going to have to figure something out because I don't have the manpower to be taking it apart all the time or with conveniently available longer arms. 

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