Alternate Names: New Zealand Kaolin, New Zealand PFC
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New Zealand China Clays claim that this is the whitest clay in the world. The white primary clay deposits mined at Matauri Bay are derived from the alteration of acid volcanic rocks. The aluminosilicate feldspar minerals in the parent rhyolite have been broken down to their constituents by low temperature hydrothermal alteration and have then reconstituted as halloysite. Thus, while often called a kaolin, technically it is a halloysite.
The company has developed a unique beneficiation process (which includes filter pressing and thus the designation PFC or Premium Filter Cake) to ensure a high degree of purity. They claim 0.1% on a 240 mesh screen. This material is exported to many parts of the world.
We have found that porcelains made using this fire a little whiter and are more translucent than with Grolleg kaolin. However that comes at a cost. As a pure material, NZK is less plastic than pure Grolleg (being barely workable enough to wedge and roll into a slab, for example). Notwithstanding this NZK produces a body that is noticeably stickier. Grolleg requires less common plasticizer addition (e.g. bentonite) to create a plastic porcelain. However NZK responds especially well to VeeGum (or similar highly refined smectites and hectorites) to create highly plastic yet very white burning porcelains. But NZK will produce a significantly less vitreous body because it comes closer to the theoretical A12O2:2SiO2 chemistry (Grolleg contains significant KNaO). That means, for example, that a cone 10 porcelain having near 50% kaolin will need 5-10% more feldspar, that will need to come at the expense of the kaolin. That will, in turn, necessitate an increase in white plasticizer (thereby increasing body cost).
The whitest test bar here is a New-Zealand-kaolin-based cone 6 porcelain (employs VeeGum for plasticity). Immediately to the left of it are three North American-koalin-based bodies using standard bentonites. The bar to is right in a Grolleg based body that uses a standard bentonite rather than a white burning one. All are plastic.
These are two cone 6 transparent glazed porcelain mugs with a light bulb inside. On the left is the porcelainous Plainsman M370 (Laguna B-Mix 6 would have similar opacity). Right is a zero-porosity New Zealand kaolin based porcelain called Polar Ice (from Plainsmanclays.com also)! The secret to making a plastic porcelain this white and translucent is not just the NZ kaolin, but the use of a very expensive plasticizer, VeeGum T, to enable maximizing the feldspar to get the fired maturity.
These bowls were made by Tony Hansen using a mixture of white and stained New-Zealand-kaolin-based porcelain (Plainsman Polar Ice) fired at cone 6. The body is not only white, but very translucent.
A transparent glazed. It is a made from Plainsman Polar Ice in 2014 (a New Zealand kaolin based porcelain) and fired to cone 6 with G2926B clear glaze. 5% Mason 6306 teal blue stain was added to the clay, then this was wedged only a few times. The piece was thrown, then trimmed on the outside at the leather hard stage and sanded on the inside when dry.
These three materials also fire to a similar color. Grolleg is the most plastic, Dragonite the least.
This cast bowl (just out of the mold and dried) is 130mm in diameter and 85mm deep and yet the walls are only 1mm thick and it only weighs 89 gm! The slip was in the mold for only 1 minute. What slip? A New Zealand Halloysite based cone 6 translucent porcelain. This NZ material is fabulous for casting slips (it needs a little extra plasticizer also to give the body the strength to pull away from the mold surface as it shrinks).
The two mugs on the left: Traditional Grolleg porcelain using Nepheline and bentonite (fired to cone 10R). The right: Using New Zealand kaolin, Nepheline Syenite and VeeGum.
The original bag of this product in 2014.
Electron micrograph showing Dragonite Halloysite needle structure. For use in making porcelains, Halloysite has physical properties similar to a kaolin. However it tends to be less plastic, so bodies employing it need more bentonite or other plasticizer added. Compared to a typical kaolin it also has a higher fired shrinkage due to the nature of the way its particles densify during firing. However, Dragonite and New Zealand Halloysites have proven to be the whitest firing materials available, they make excellent porcelains.
These balls are easily broken down by the propeller in a slurry mixer. But they do not break down easily in a dry mixer, even when in a mix with other materials (like silica and feldspar). They just bounce around on a vibrating screen. That means that without some sort of finishing device in the dry material feed stream to break down these lumps before the pugmill, it is difficult to manufacture homogeneous plastic body employing it.
Left: Cone 10R (reduction) Plainsman P700 porcelain (made using Grolleg and G200 Feldspar). Right: Plainsman Cone 6 Plainsman Polar Ice porcelain (made using New Zealand kaolin and Nepheline Syenite). Both are zero porosity. The Polar Ice is very translucent, the P700 much less. The blue coloration of the P700 is mostly a product of the suspended micro-bubbles in the feldspar clear glaze (G1947U). The cone 6 glaze is fritted and much more transparent, but it could be stained to match the blue. These are high quality combinations of glaze and body.
The recipe: 50% New Zealand kaolin, 21% G200 Feldspar, 25% silica and 3% VeeGum (for cone 10R). These are the cleanest materials available. Yet it contains 0.15% iron (mainly from the 0.25% in the New Zealand kaolin, the VeeGum chemistry is not known, I am assuming it contributes zero iron). A 50 lb a box of pugged would contain about 18,000 grams of dry clay (assuming 20% water). 0.15% of 18,000 is the 27 grams of iron you see here! This mug is a typical Grolleg-based porcelain using a standard raw bentonite. A box of it contains four times as much iron. Enough to fill that cup half full!
Out Bound Links
From a purely physical properties point-of-view, halloysite is a clay mineral similar to kaolin in firing and raw appearance. In fact, it normally occurs with kaolin deposits because kaolin is the pre...
Veegum T, Veegum CER, Veegum Pro, VGT
Grolleg China Clay
In Bound Links