The thorough blending and grinding of glaze and raw materials can yield consistent results in a finished glaze.
Glaze mixing is a central component in many ceramic
operations. The labor-intensive steps involved in forming, glazing and firing
ceramic ware can often be negated by a single error in the glaze mixing
process. Essentially, glazes are composed of alumina and silica combined with
fluxes in varying ratios to form a vitreous glass surface when heated.
While numerous raw materials are finely ground at the
mine or processing plant, some are not, and coarse materials can result in
glaze imperfections. A thorough blending and grinding of raw materials can
yield consistent results in the finished glaze. Based on a proven grinding
method, a new glaze mixer* uses a ceramic mortar and pestle operated by an
electric motor. When the revolving pestle comes into contact with the ceramic
bowl, raw materials are mixed and reduced in particle size, which can have a
dramatic positive effect on the fired glaze.
Small test batches (0.5-9 oz) can be placed into the bowl
either wet or dry. The mixer is ideally suited for use in the potter's studio,
allowing for the consistent blending of small test batches of glaze or the
grinding of raw materials.
* Available from Nidec-Shimpo America Corp., Itasca, Ill.
Figure 1. Natural bone ash before (left) and
after grinding in the mixer for 1 hour.
An Even Mix
A direct relationship in ceramic materials exists between
particle size and the material's ability to melt when subjected to heatwork
within the kiln. Large particles, having less surface area, do not melt as
readily as smaller particles, which have greater surface area. Raw materials
stone, borax, gerstley borate and natural bone ash clump together in storage
and do not easily merge into a glaze mix (see Figure 1).
Often, large particles do not blend uniformly, causing
defects in the fired glaze. This effect is also noticeable with metallic
coloring oxides, which can have relatively coarse particles in comparison to
their finer carbonate forms. The action of the new mixer grinds and blends
glaze materials to provide uniform color and raw material distribution.
The glaze mixer's dimensions are 8.5 x 13.75 x 24.5 in.,
and the mixing bowl is 6.5 in. wide. The mortar mixing speed is 7 rpm, while
the pestle's speed is 115 rpm. These speeds provide for the controlled formulation
of ceramic raw materials.
Figure 2. Glaze samples on the left of each
photo were not mixed with the new mixer. Defects include a) black iron oxide
specking, b) chrome oxide specking and c) nepheline syenite specking. Glaze
samples on the right were mixed with the new mixer and show no glaze defects.
Put to the Test
The new mixer was recently tested with three glaze
samples (see Figure 2). All of the glazes were applied to vertical test tiles
and fired to c/06/ox (1828°F). The mixed glazes reduced the particle size of
black iron oxide, chrome oxide and nepheline syenite in the three glaze
The tiles on the right side of each image represent
thoroughly mixed glazes that were placed in the new glaze mixer, which provided
an even dispersion of metallic coloring oxides and raw materials.
A studio potter's ability to produce reliable results is
an important factor in any successful ceramic endeavor. It is often said that
the only thing consistent about ceramics is its inconsistency. While many raw
materials are processed for direct use by potters (in terms of particle size),
some of the most widely used materials surprisingly still need a finer degree
of processing. The glaze mixer is a useful tool in eliminating one source of
inconsistency by efficiently grinding and blending ceramic raw materials.
For additional information regarding the glaze
mixer, contact Nidec-Shimpo America Corp., 1701 Glenlake Ave., Itasca, IL
60143; (800) 237-7079 or (630) 924-7138; fax (630) 924-0340; e-mail email@example.com;
or visit www.shimpoceramics.com.