Line Blend Glaze Testing

     In glaze testing, sometimes finding a color or glaze surface you like can be a challenge. Line Blending, with all its variables, can assist in making it less so. Line Blending is basically a way to gradually change variables in a glaze recipe. The most simple line blend is a Single Variable Line Blend:

     In a Single Variable Line Blend you increase the percentage of something in addition to the 100% recipe. This makes Single Variable Line Blends incredibly helpful in finding the right amount of colorant or opacifier you'd like in a glaze. The numbers at the top of each figure is the number of each tile. For this type of line blend, A represents a base glaze and B represents an additive. Taking a clear glaze and adding percentages of Red Iron Oxide, for example, could take you from a celadon to an amber to a Tenmoku (However I'd increase the percentages by .5% instead of 1%). The percentages show above are just listen to illustrate the idea, but you can change the increments between each tile by any amount. 

     The easiest way I've found to do this type of line blend, rather than mix up seven separate glaze slops, is to mix a 500 gram batch of the base and dip tile 1, then add 1% of the additive and dip tile 2, add another 1% of the additive and dip tile 3, and so on until finished. Obviously, this is not exact because you take away some of the base with each dip, but its close enough to get you in the right area for the color you're looking for.

     The next form of Line blend is a Double Variable Line Blend. This line blend is good for mixing two additives (Copper Carbonate and Tin Oxide for example) to find the right mix of both. This type of line blend, as well as all of the following line blends are completed using a much different process than a Single Variable Line Blend. For this, and all of the following blends, you mix up a glaze slop of the base for each letter. Then in each glaze slop you add whatever you'd like to be blending. The more tiles you will be dipping the larger of a glaze batch you'll need to make. 

     For example, you could have two 500 gram batches of:

Custer Feldspar - 34

EPK - 33

Whiting - 33

    In one batch you add 5% Red Iron Oxide (which would be 25 grams) and in the other you add 10% Titanium Dioxide (which would be 50 grams). Then you use a spoon to take the proportion of each batch into the mix - Tile 5 for example would be two spoonfuls of batch A and four spoonfuls of batch B. This is demonstrated in the image below. Thoroughly stir the mix and dip your tile.

  

   To calculate the recipe of a single tile, follow the image below.

     The following types of line blending are all complete the same way as Double Variable Line blends, however they require increased amounts of glaze slops (Biaxial and Triaxial require three, and hexaxial requires six).

     The Hexaxial Line Blend is a beast of my making. If you're looking for a specific glaze base you can put one material on each corner and blend them to find 37 different bases. Most of them might not work, but this allows you to see lots of different bases all at once. It also works just like any other line blend and you can have one base with 6 different additives.
     The reason the tiles skip numbers unlike the previous line blends is that it would require an enormous amount of tiles to make it have smaller increments, but line blending is a general experiment anyway. As you do line blends and become more particular with what you're looking for you can hone in on the area of a line blend you like the most.

     If you have questions please feel free to ask, and if you have tested any of these (especially the Hexaxial) and would like to share please do!

Material Information: Wollastonite

The acicular nature of Wollastonite's crystals

50/50 Base
Neph Sye - 50
Wollastonite - 50

50/50 Base + Copper
Neph Sye - 50
Wollastonite - 50
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Copper Carb - 2% 

Shorn Base + Copper
Wollastonite - 25
Spodumene - 25
Cornwall Stone - 25
Talc - 25
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Copper Carb - 4%

Shorn Base + Cobalt
Wollastonite - 25
Spodumene - 25
Cornwall Stone - 25
Talc - 25
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Cobalt Carb - 2%
Copper Carb - 1%

     Wollastonite is a natural mineral made of Silica and Calcium (CaSiO3) that is acicular - meaning that the crystals that make up Wollastonite are needle like (above). Because of this unique structure and chemical makeup there are a few things that Wollastonite can do that are quite interesting:
     1. The crystaline structure of Wollastonite can produce visible crystals in a fired glaze, seen in the Shorn glazes (below right), when the base glaze is low in alumina - the higher alumina will stiffen the glaze melt in such a way that the crystals cannot form
     2. The crystaline structure of Wollastonite holds onto itself allowing the dry material to be lifted fingers down, in the same way that straw can be lifted fingers down
     3. The fibrous form of Wollstonite is a good additive in low fire clay bodies because it promotes low thermal expansion and reduces drying and firing shrinkage
     4. Wollastonite is an excellent source of Calcium - a strong flux - for glazes that does not bubble during the firing due to off gassing whereas Whiting, the other prominent source of CaO, produces bubbles in the glaze from off gassing

Chemical Differences: Rutile and Ilmenite

        Titanium Dioxide helps to form crystaline structures in glaze melts. The most common materials added to glazes to introduce TiO2 are Titanium Dioxide itself, Rutile, and Ilmenite. Both Rutile and Ilmenite contain a significant amount of TiO2. However, Ilmenite contains more "contaminants" compared to Rutile. On a simplistic level, Ilmenite contains approximately 50% FeO whereas Rutile only contains about 10% Fe3O2. Both also contain other contaminants that are in minute levels.

http://digitalfire.com/4sight/material/rutile_1204.html

http://digitalfire.com/4sight/material/ilmenite_863.html

Rutile: 
Can be found in granular or powdered form. The varied size varies the mottling in the glaze. The most commonly produced colors by Rutile are tan and blue (seed of the glaze name "Rutile Blue"). The Titanium Dioxide in it can inhibit crystal formation (see Permafrost Base, Rutile Line Blend) and the iron in the material can help in fluxing the glaze at high levels. Rutile can also be used to soften the color producted by more potent colorants such as Chrome and Cobalt and variegate the both the texture and color in a glaze (see Satin Base Green).


Ilmenite:
Also can be found in granular or powdered form, however is more common in granular. Can be used in clay bodies or glazes to produce a speckled effect. Like Rutile, can seed Titania crystals in a glaze. The higher amounts of iron in the material can help to flux. Grains of Ilmenite in a glaze can bleed out at higher temperatures, forming dark blemishes. In combination with Rutile, Ilmenite can help to produce the characteristic Rutile streaking and mottling.