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Boraq 1

A plastic native mineral souce of boron for glazes. A compound of materials that is chemically, mineralogically, and physically very similar to what Gerstley Borate was.

Boraq is a source of boron (a low melting glass) for use in glazes. The boron content is high enough that the Boraq begins to melt below cone 010, thus it can be used as the primary flux in low fire glazes and as a secondary flux in stoneware glazes. Unlike frits, Boraq is plastic. Thus it suspends, hardens and fluxes glazes. Boraq based glazes thus do not necessarily need any other clay materials in the recipe.

Since Boraq is a mineral compound, it has a complex melting process that is very unlike that of frits. Colored and partly opacified glazes employing Boraq can thus have a much more interesting variegated surface. At middle temperature stoneware glazes employing Boraq form a melt composed of the more fluid boron and less fluid fluxes like soda, potash, and calcia. These multiple melt phases add to the variegation that is frozen into the glaze as it cools.

Comparing to GB

For users accustomed to working with Gerstley Borate there are a number of factors you should be aware of when using Boraq:

-Boraq creates a glaze that requires about the same amount of water but the slurry gels less giving it better flow and thus better application properties (it still gels enough to prevent running and dripping). After an overnight sit the Boraq containing glaze will settle (leaving a layer of water at the top) and then gel slightly. It is easier to remix and you can remove water if needed (GB glazes gel so much that they do not tend to form the layer of water even if they contain too much water).

-Boraq glazes build up a layer on the ware faster, thus you do not have to hold them in the glaze as long. However it is easier to get Boraq glaze on too thick. Bisque ware will not become as waterlogged and the glaze dries faster (although still much slower than typical fritted glazes). The hectorite in the Boraq recipe is responsible for this behavior, we believe it is about right.

-Boraq glazes still bubble and blister if applied thickly and fired quickly, but not nearly as bad as Gerstley Borate ones.

-High Boraq cone 6 glazes have the same tendency to run during melting as Gerstley Borate ones.

-Boraq has the same tendency to produce variegated surface effects and responds to small amounts of lithium to heighten the effect. Infact it appears to be an even better variegator.

-Boraq 1 does not produce the intensity of red in iron red glazes as easily (it tends toward dark red and maroon). See below for more info. Boraq 2 and 3 do produce reds.

-Boraq 1 has a higher formula weight than GB so less may be needed in your glazes. However it does not fuse as early so a little more may be needed to melt. Thus it appears the it is a one-for-one substitute.

-Boraq 1 does not melt into a transparent glass as early as Gerstley Borate, however it 'catches up' and fuses most glazes from cone 06 and up the same as GB.

Comparing to Other Subs

Many substitutes are on the market now and the details of these are discussed on the website at www.gerstleyborate.com. We believe that Boraq is the best because it addresses three key factors:

Mineralogy: Boraq contains the minerals that Gerstley Borate did (Gerstley was a compound of minerals). Although the chemistry of the overall mix can be put into a frit, that frit will not have the same melt character. In addition, substitutes that do not consider this factor will have different working characters.

Chemically: The chemistry of Boraq is closer to Gerstley Borate than the others. Frits cannot be made with as low silica and alumina as Gerstley Borate without being soluble. Many of the substitutes have chemistries that are quite radically different because formulation effort focussed on achieving similar physical melting character. However color and surface are matter of chemistry, thus these substitutes do not work with many colored and textured or matte glazes.

Physically: Gerstley Borate contained significant plastic clay, thus it imparted a working character to glazes that made them easy to apply and store. Most substitutes do not consider this factor and suppliers simply recommend adding clay. However this advice ignores the fact that the added clay changes the chemistry of the glaze (a signficant amount of clay is needed if the glaze depending whole on GB for suspension and hardening).

There are several other important differences with Boraq:

-Information on its chemistry and recipe are freely available.

-It is supported at its own website.

-It is not a one-mix-for-all-situations material, we recognize that such a solution is very unlikely to surface and that we must adapt the material to each circumstance.

Boraq 2 and Boraq 3

We realize that one version of Boraq is not going to work in all recipes. Thus we have defined two variations.

-Boraq 2 is 84 parts Boraq 1 plus 8 whiting and 8 dolomite.

-Boraq 3 is 84 parts Boraq 1 and 16 whiting.

Here are the suggestions for substituting Boraq for Gerstley Borate in glaze recipes:

-Use Boraq 1 for low temperature glazes first. It melts the best. If it melts too much or colors are not right, try Boraq 2.

-Use Boraq 2 first for medium and high fire glazes. If color needs calcium to develop (i.e. chrome-tin pinks) then try Boraq 3.

Formulating with Boraq

Like Gerstley Borate, Boraq melts so well that it is possible to mix it with almost any other ceramic material to form a glaze. While students thrive on the ease with which visually interesting glazes can be formulated it must be recognized that glazes with unbalanced chemistry are much more likely to be leachable and lack hardness. We recommend that you have your glazes tested for leaching and hardness if they are being used on food surfaces. In addition, glazes with significant amounts of Boraq will be fluid and tend to run off ware onto kiln shelves.

Chemical Analysis

 CaO      17.7
 K2O       0.5
 MgO       2.5
 Na2O      3.5
 SrO       0.3
 B2O3     34.4
 Al2O3     2.1
 SiO2     13.4
 Fe2O3     0.1
 LOI      25.4%

Support

Getting a Sample

This material is available on-line at axner.com (Orlando, Florida). Just go into their store and click on the "Supplies" link at the top, then on "Glaze and Clay Body Materials" (or use the 'search' function). They will ship around the world. If you are in Canada please fill in the form below.

We are working on setting up dealers for this material and will post this information here when available.

MSDS

A detailed Materials Safety Data Sheet (MSDS) is available for this material. To view it Click Here. To download the Acrobat file to your computer, Right-Click Here for Windows or Hold-Click Here for Macintosh. A menu should pop-up that will give you an option to download the file.

News

Boraq 1 is our benchmark material. However we know that it does not work in some glazes at cone 6. Thus we are recommending additions of 8 whiting and 8 dolomite (Boraq 2) for testing. The particulars are thoroughly discussed at http://www.gerstleyborate.com.

Plainsman Clays Ltd.
Box 1266, 702 Wood Street, Medicine Hat, Alberta T1A 7M9
Phone: 403-527-8535 FAX: 403-527-7508

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