Replacing Materials that Are No Longer Produced or Have Changed Greatly

[George Lewter]

In the last couple of decades we have seen a number of materials that were in widespread use by potters suddenly go out of production. One of the earliest in my recollection was Albany Slip which provided the brown glaze on porcelain electrical power line insulators across North America for more than a century. It seems that the rate at which standard materials are disappearing has been accelerating in the last few years. Gerstley borate is a material that was discontinued, caused massive distress in the pottery community, and was actually put back into production after raw stockpiles were found and purchased by Laguna Clay Company.

G-200 feldspar ran out and was replaced with a different formulation, G-200HP. Kona F-4 feldpar is gone, as is Cornwall Stone and other materials seem to be going at such a rate that it is getting hard to keep track. 

This discussion topic is a place to note common materials that are becoming scarce or unavailable, and to post the best available substitutes for them. It is not intended to be exhaustive, because that is already a mission of Tony Hansen and the digitalfire Ceramic Materials Database. It is intended only to be a quick reference for major ceramic materials that may be disappearing. 

[George Lewter]

Cornwall Stone Substitute - Digitalfire

Cornwall Stone is no more. Make your own.

Code Number C6S-1003

Batch Number 0

Owner: Norm Stuart

Materials	Amt
Custer Feldspar	30.40
Silica	29.30
Nepheline Syenite	23.80
Kaolin	12.90
Wollastonite	3.30
Dolomite	0.37

Total:100.07

Pictures

Recipe Notes

Ever since 1807, Cornwall Stone has a changed chemically depending on where the miners were digging.

Now the original mine is closed and gone.

Fortunately Tony Hansen at Digitalfire has created this recipe which is inexpensive and perfect every time.

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Born: 2013-08-20, Modified: 2013-08-21 00:18:06

[Norm Stuart]

Although U.S. Feldspar discontinued blending feldspars into G-200 (potash feldspar) Laguna Clay has picked up where they left off which they sell as G-200 Old Blend.  http://www.axner.com/feldspar-g200-old-blend.aspx

The formula is simple:  70%  G-200HP and 30% Minspar 200.

The 300 tons of newly blended Gerstley Borate has a different chemistry from that listed on Digitalfire.  For our uses I don't notice a difference.  I find 2/3 Gerstley Borate and 1/3 Mason Stain makes the ideal suspension for color concentrates people at our studio either use an an underglaze or as tints for clear, white or semi-matte base glazes.

http://www.axner.com/gerstley-borate.aspx   

New Chemistry:  http://www.axner.com/pdf/laguna/Chemical_Composition_of_Gerstley_Bo...

[George Lewter]

Kona F-4 feldspar (no longer produced) can be replaced by a one for one replacement with Minspar 200, which according to digitalfire has virtually identical chemistry. Reference material chemistrys are available to us on the Insight-Live database. Very handy when modifying and substituting materials in a glaze recipe.

[Kathy Griffith]

This is absolutely great information!  I'm saving this!

[Lawrence Weathers]

 

 

I contacted Johnson Matthey asking where I could buy their MOK-623 frit in the US.

This is what they said

 

 

"I am searching through all or our product lists and to date we do not know  this product.

It was either a special development that is no longer available, is no longer a JM product (sold when sectors have been spun off) or has never been a JM product.

 

As stated so far I have had no luck but my search will continue"

 

 ..... Bummer.....

[Norm Stuart]

I have a substitute for Johnson Matthey Frit 623  aka (B33X7, MOK623) in the Insight Live Database.

Although Alisa Clausen used this frit because she could not source Ferro Frit 3134 at the time, the result of using Frit 623 with added Barium and Zinc, with less Calcium, produces very interesting effects in some glazes - such as Cassie's Marsala.

Lawrence Weathers said:

I contacted Johnson Matthey asking where I could buy their MOK-623 frit in the US.

This is what they said

"I am searching through all or our product lists and to date we do not know  this product.

It was either a special development that is no longer available, is no longer a JM product (sold when sectors have been spun off) or has never been a JM product.

As stated so far I have had no luck but my search will continue"

  ..... Bummer.....

[Lawrence Weathers]

that looks good. let me know how it actually works.

thanks for your hard work on this.

[Norm Stuart]

Regarding the MOK-623 Frit Alisa Clausen used when making "Cassie's Marsala".  Cassie's Marsala

I'm confident that Alisa's test tile was made with a much lower percentage of iron oxide than using high purity iron oxide and I suspect her kiln fired somewhat hotter than Cone 6 degrading the Fe2O3 red iron oxide into Fe3O4 black iron oxide.

The chemistry of this glaze is similar to Vee's Tenmoku Gold which develops Iron Silicate crystals.  By themselves these are red like this Fayalite from Germany, but when crystallized with calcium and magnesium iron silicates become yellow like this Nephrite Jade from Wyoming.

Vee's Tenmoku Gold - undegraded red iron oxide capped with calcium-magnesium-iron silicate crystals.  Hotter areas of the tile have seen red iron oxide degrade to black iron oxide.

Making a "chemically identical" glaze to the Cassie's Marsala Alisa made using MOK-623 frit and high purity red iron oxide, I end up with too much red iron oxide and the glaze becomes opaque, even with a very slow-cool. 

But a portion of the glaze (blue arrow) has already begun to form the gold calcium/magnesium iron silicate.  On the far right, being fired only to Cone 04, the chemically identical glaze is only partially melted and very opaque like a poster paint, whether 1,2 or 3 dips.

So the iron has to be removed as iron-calcium-magnesium-silicate crystals to leave areas of clear silica glass - as they have on Alisa's tile on the left side

This tile below, of Cassie's Marsala using Ferro 3134 Frit and Laguna's low-quality red iron oxide, containing up to 15% barium sulfate actually comes closer to Alisa's tile, and in fact close to her chemistry with the added barium found in the MOK-623 frit and a much lower level of actual red iron oxide.

I'd suggest making the "chemically identical" glaze without the red iron oxide, relying only on the iron in the Redart Clay.  There' is probably more red iron oxide in Alisa's tile than that, but not as much as 6.6% of high purity red iron oxide.

Lawrence Weathers said:

that looks good. let me know how it actually works.

thanks for your hard work on this.

[Dani Montoya]

Wonderful information. Thanks