Helmer Kaolin

Smooth very clean white burning halloysite (kaolin-like) mineral. Raw Helmer Kaolin clay is a white burning material that contains very little physical contaminant and we process it in no other way than simple grinding. The raw lump form is comparatively white and clean. In the quarry the seam of clay contains some isolated stringers of darker burning iron material, these are ground and blended with the rest of the material.

Mineralogically, Helmer kaolin contains kaolinte and halloysite clay minerals (and small amounts of others of course). Its halloysite content is one of the factors that makes it useful for certain special purpose non-ceramic applications. Plainsman does not currently monitor the mineralogy (e.g. halloysite content) of this material.

Helmer Kaolin is prized by potters for its flashing properties during firing (flashing refers to brown and red surface coloration on unglazed areas that develops during wood firing). The chemical or physical phenomena responsible for this behavior has not been clearly explained and there is much disagreement in currect speculation.

Helmer kaolin was used for many years in the refractories industry. It was calcined to produce low-quartz thermal-expansion-stable aggregate used to make kiln furniture.

Process Properties

The physical properties of Helmer kaolin are similar to typical commercially available medium plasticity kaolins. In raw form it is quite white and has a plasticity lower than a typical pottery clay.

Like any kaolin, it has a high water of plasticity (26-28%) and LOI and it has an ultimate particle size that is significantly larger than ball clays and bentonites. Additions of Helmer kaolin to bodies made from other Plainsman native clays helps diversify the ultimate particle size distribution to produce whiter bodies with better drying properties, greater fired strength, and higher maturing temperatures.

Firing

Helmer kaolin has a fired shrinkage that is higher than typical kaolins, even if fired to temperatures far below its maturing range. This is because of the shape of the halloysite mineral particles it contains and the way these collapse and pack during firing. Thus there is some need for caution as to how much is used in a body. However if other materials in the recipe have ranges of particle sizes that complement it fired shrinkage will be minimized.

Since Helmer kaolin is not ground to 200 mesh as other industrial minerals we do not recommend its use in porcelain bodies without further processing because there could be some isolated iron specks that show up in firing, especially at higher temperatures.

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.

Physical Properties

 Drying Shrinkage: 5.5-6.5%
 Dry Strength: n/a
 Water Content: n/a
 Drying Factor: C120
 Dry Density: 1.75

Sieve Analysis (Tyler mesh):

     +100: 0.5-1.5%
 100-150: 0.5-1.5
 150-200: 1.0-2.0
 200-325: 2.5-4.5

Fired Shrinkage:

   Cone 6: 10.0-12.0%
   Cone 8: 11.0-12.0
  Cone 10: 12.0-13.0
 Cone 10R: 12.0-13.0

Fired Absorption:

   Cone 6: 7.0-9.0%
   Cone 8: 4.5-5.5
  Cone 10: 2.5-4.0
 Cone 10R: 2.5-4.0

Chemical Analysis

 CaO       0.2
 K2O       0.6
 MgO       0.2
 Na2O      0.1
 TiO2      1.2
 Al2O3    33.1
 P2O5      0.0
 SiO2     49.0
 Fe2O3     1.1
 MnO       0.0
 LOI      14.5%

Plainsman Clays Ltd.
702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535 FAX: 403-527-7508
Email: plainsman@telus.net

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