Glazy Video Tutorials

New video tutorial “Creating Analyses & Deriving Recipes on Glazy.” In this tutorial, we’ll use Glazy (glazy.org) to create an analysis of an ancient celadon glaze from Nigel Wood’s book “Chinese Glazes”, and using that analysis create an actual glaze recipe that we can test in the kiln.

https://wiki.glazy.org/t/glazy-help-index/

#glaze#glazes#glazerecipes#ceramics#pottery#ceramicglazes#glazechemistry#glazy

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Can you leave Jingdezhen?

“Can you leave Jingdezhen?”

This has been an important question for me during over a decade of study in Jingdezhen, China. In the “Porcelain Capital of the World” it’s easy to find anything you could dream of- the whitest, most translucent porcelain clay, glazes of all types and colors, kilns of all shapes and sizes. The city is filled with master artisans who can help you make anything you dream, from 2-meter tall Buddhas to delicate miniature porcelain flowers.

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Mary Fox Pottery

Through Glazy I’ve met amazing people all over the world, most recently @maryfoxpottery

It’s impossible to even begin to represent this artist through a few images in an IG post.  A self-taught potter who’s supported herself through ceramics since 1979, it’s astonishing to me how a single person can be so prolific, simultaneously producing multiple lines of work (from beautiful, simple functional ware to large, technically demanding decorative and sculptural forms including her exquisite “chalices”) each in a broad range of ceramic bodies, firing temperatures and glazes- and ALSO in glass!  And did I mention she is writing a book?! Mary has been generous with her knowledge through her lectures and workshops, and she’s also sharing some of her favorite recipes on Glazy.  Please visit her Glazy home at https://glazy.org/u/maryfoxpottery

Please follow @maryfoxpottery for more beautiful images of her work as well as announcements for upcoming events and her new book!

#glaze#glazes#glazerecipes#ceramics#pottery#ceramicglazes#glazechemistry#glazy

Colored Mason Stains in Porcelain Slips

I’ve added some simple slip recipes to illustrate how one can use the Mason Stains added yesterday.  These slip recipes use a material called “English Porcelain”, which is simply an analysis of a typical high-fire porcelain body, as well as 8-10% added Mason Stain.  I hope you will add color tests, too!

You can find these slips in the “Slip & Engobe” section or visit the collection here:  https://glazy.org/u/derekau?collection=7661

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Crazing: Fixed Glaze, Variable Body

Here’s another test with fixed glaze and variable body.  The glaze is @pete.pinnell Pinnell Blue Celadon (a fairly low-expansion glaze that does not usually craze on porcelain bodies), while the porcelain is a typical high-fire body with Red Iron Oxide (RIO) successively added in 1% increments. Fired in a reducing atmosphere to Orton cone 10. 
Without RIO, this glaze fits the body perfectly.  After adding just 1% RIO to the body we can already see slight crazing, while at +2% RIO the glaze is completely crazed.

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Adjusting Clay Body to reduce Crazing

(Disclaimer: I’m not a clay body expert!) Rather than a biaxial with changing glaze chemistry applied to a single clay body, here is the opposite:  A biaxial with fixed glaze (Nigel Wood’s Jun) and variable stoneware clay body, with increasing Alumina moving up and increasing Silica to the right.  This test demonstrates that crazing is a function of the thermal expansion of both clay body and glaze.  If you can’t get a glaze to fit you may want to change the body, instead, although adjusting the body may lead to other issues like dunting. 

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Val Cushing’s Handbook

Repost from @alfredceramics.  Leave it to the amazing people at @alfredceramicsto turn test tiles into freaking ART!  These are the most beautiful test tile photos I’ve ever seen.  @earlyamericanrobotpotteryblew my mind: “We’re using these glazes on our artwork, so why not photograph the tests the same way we photograph our ceramics?” The completed sets of cone 6 and cone 10 glazes from Val Cushing’s Handbook represent hundreds of hours of work by Keith Simpson and Rachel Allstadt @luxmud and are an example for all of us to emulate.  Download the PDF’s and check out the images in full resolution.

http://www.alfredgrindingroom.com/raw-materials/

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Cone 6 Oxidation Blue Triaxial Blend

In Chinese Glazes, we learn from Nigel Woods that the cobalt used for underglaze blue & white underglazes and blue glazes came in a range of chemical compositions and grades of purity.  Thus, there are many shades of blue due to the quality of cobalt-containing stone as well the overlying glaze.

In the same book, Nigel presents a lovely Chinese blue stoneware glaze which, in addition to cobalt, contains iron and manganese “impurities”.

In fact I’m personally not fond at all of glazes and underglazes containing only cobalt as a coloring oxide.  Pure cobalt often comes out as a garishly blue color.  In the triaxial blend below, I take a nice clear glaze (Sue’s Clear) with added 1% Cobalt Carbonate.  Then I blend with 1.5% Red Iron Oxide (bottom left) and 1.5% Manganese Dioxide (bottom right).  The resulting colors on the bottom row are much more pleasing to my eye.

The full image can be viewed here:  http://www.derekau.net/wp-content/uploads/2014/12/BLUE_TRIAX_ALL.jpg

Orton Cone 6 Clear Glazes

Having not fired cone 6 since college, I started by first testing a number of clear cone 6 glazes on https://glazy.org

I also studied up on cone 6 glaze chemistry via Matthew Katz​’s Advancing Glazes course and his papers: Boron in GlazesMid-Temperature Glaze ScienceGlaze Safety/Durable Glazes Presentation.

Click here for full image of cone 6 clears.

Out of these tests, there were two glazes that I preferred.  The first, Sue McLeod​’s Clear, is a soft clear with minimal clouding and has B2O3 at 0.18 which, according to Matt’s information, is ideal for cone 6 glazes.

The second glaze is a shop glaze available at the Wellsville Creative Arts Center called WCAC Celadon Clear.  With B2O3 at 0.45, it is really high in boron and possibly less durable than the lower-boron clears I tested.  However, WCAC Celadon Clear is by far the clearest glaze I’ve tested, almost like a layer of pure glass or honey.  Even on dark stoneware it’s really clear with almost no clouding.

Being new to cone 6, I was curious as to the effect of boron levels on clear glazes.  So, I created two biaxials, both with R2O fixed at 0.2.  In the first Sue’s Clear inspired biaxial, B2O3 is set at 0.18.  In the second biaxial inspired by Celadon Clear, B2O3 is doubled to 0.36.

Each biaxial resulted in a nice clear, with the higher Boron clear being almost completely transparent and glossy, while the Boron 0.18 clear is translucent and soft.

Standard Cone 6 Porcelain Body #551

Link to full-size image here.

Same chart but with words describing each test glaze:

The best clear resulting from the B2O3 0.18 biaxial is here: C6 R2O 0.2 B2O3 0.18 Best Clear

In order to test the effect of higher B2O3 levels, I doubled the amount of Boron in the initial biaxial from 0.18 to 0.36 while maintaining the same R2O:RO ratio.  I also made the boundaries of the tests a little higher (see map comparison).  I was surprised to see that the only clear glazes in the 0.36 Boron test appear much farther down (lower in Si & Al) in the chart.  But the “clear” region is still in the same Si:Al Stull region.

Link to full size image here.

The best clear resulting from the B2O3 0.36 biaxial is here: C6 R2O 0.2 B2O3 0.36 Best Clear

It is similar to WCAC Celadon Clear in it’s glossy, transparent quality.

High-Boron Clears

After testing WCAC Celadon Clear and seeing the results of my B2O3 0.36 biaxial, it seems there is definitely a region of very glossy, very clear glazes at higher boron levels.

Coincidentally, I tested an old glaze recipe posted to the Clayart mailing list by Laura Speirs in 1996:  https://glazy.org/recipes/21102  As with the WCAC Celadon Clear, the Speirs recipe is also very high in Boron (0.51), and it also fires very clear and glossy:

VC Easy Glossy

One afternoon I began discussing the WCAC Celadon Clear with a WCAC member, Nancy Alt.  I was very surprised to discover the interesting history of this glaze.

In 2009 Nancy Alt had visited Val Cushing’s home and purchased a vase with a lovely blue-green celadon glaze. Nancy asked Val if he could share the glaze recipe, and he not only shared it but converted it from cone 9 to cone 6 (the temperature Nancy was firing). Val’s email is copied below. It shows the extremely generous nature of this amazing potter and teacher:

From: Val Cushing

Subject: Re: celedon glaze

Date: May 12, 2009 at 12:46:57 PM EDT

To: Nancy Alt

Dear Nancy,

This glaze is one I made for C/9 oxidation electric firing, so that it would appear to be a blue green celadon. I have revised it for you to be the same color and texture only for C/6 ox. electric . I will give you two to try , first VC Pale Emerald, C/6 , glossy , blue/green , celadon looking. as follows………. Kona F/4 feldspar 24, Ferro Frit 3134 24, Dolomite 4, whiting 14, barium carbonate 2, zinc oxide 2, flint 24, and EPK 6. ADD TO THAT , 1/2 % COPPER CARBONATE for blue green. VC/easy glossy, C/6 ox. , electric , celadon looking , green. Cornwall Stone 46, Gerstley Borate 20, Ferro Frit 3124 26, Ball Clay 8. — add 2% copper carb. and 1/2 % red iron oxide for celadon looking green color. Test these two Nancy and if the color is not exactly what you expected let me know and we can make a revision. We may have different “tastes” about color , but we can get what you want…My pale emerald should be quite a bit like the glaze on the jar of mine you now have. and THANK YOU . Val

So it turns out that the glaze I liked so much, WCAC Celadon Clear, was actually a Val Cushing recipe called “Easy Glossy”.  I checked Cushing’s Handbook for the recipe and didn’t find it.  Nor could I find similar recipes in the Glazy database.  So it’s quite possible this is a newly discovered Val Cushing glaze recipe.

However, the WCAC Celadon Clear had been modified from the original “Easy Glossy”, most notably subbing Gerstley Borate for Gillespie Borate.  I wanted to see not only the original recipe but also the color variations that Cushing was working with.  So I created a triaxial blend.

Below is the triaxial blend using Copper Carbonate and Red Iron Oxide.

Click here for Val Cushing’s “Easy Glossy” on Glazy.org

Click here to download full size image.

Resources

Matt Katz’s Glaze Safety & Durable Glazes Presentation, NCECA 2016

Matt Katz Understanding Glazes Online: Boron

Matt Katz Boron in Glazes