Alumina is used in ceramics in the formulation of clays and glazes. Because of its very high melting temperature it is useful for kiln wash and wadding and for atmospheric firings, to protect shelves and ware from damage from melting glaze in the kiln.
As an addition to glazes, alumina promotes matte textures, and in small quantities can promote pink color in Chrome-Tin glazes. Alumina is one of the chemicals used to create pink color in mason stains.
The word Alumina is derived from the Post Classical Latin origin Alumen, meaning bitter salt. This likely comes from the Astringent, Alum, an old French word for a material used for tanning leather, paper sizing, and other industries.
Goatskin leather glove tanned with Alum
As with most of the materials we use in the studio, Alumina is bought from Rocky Mountain clay in Denver. Rocky Mountain purchases the material from Laguna Clay in California, a large distributor of ceramic materials and supplies.
Laguna clay currently purchases this Alumina through the company, Rio Tinto, a large multinational corporation and the second largest producer of metals in the world.
The headquarters of the Aluminum division of Rio Tinto is located in Montreal Canada, and a large refinery is located north of Montreal in Alma Quebec, on the Saguenay River. This is most likely where the Alumina we use in the studio is refined.
Rio Tinto / Alcan Aluminum refinery in Canada, located on the Sauenay River in Quebec
The Rio Tinto/Alcan refinery in Alma is a massive Aluminum refinery responsible for about 1/2 of all the corporation’s global aluminum production. Here aluminum is produced for a wide range of uses – from aluminum cans to aerospace applications. Alumina Hydrate used for pottery applications represents a tiny fraction of the production of this huge global refinery and research facility.
Aluminum is produced from the raw material bauxite, an amorphous clayey rock that is rich in Alumina. Most of the world’s Alumina come from just a few large bauxite mines. Our alumina is most likely refined from Bauxite mined through an enormous international mining operation, MRN or Minorocao Rio do Norte, located in Porto Trombetas, in the Brazilian Rainforest.
Bauxite in its raw mineral form
Bauxite is extracted from the rainforest through a process in which the forest covering is removed so the bauxite rich layer of soil can be excavated. While the current practice of MRN is to carefully then replace/replant the forest after the Bauxite has been removed, mining operations have had a significant impact deforestation of the Amazon.
In addition to the contribution to deforestation and loss of biodiversity the bauxite mining in Porto Trombetas has also contributed to pollution of water systems with mine tailings.
While the mining operation in Porto Trombetas has created relatively well paying jobs, and contributed to social fabric in some ways, including building schools for employees of the mine, the mining operation has also had a profound impact on the lives of indigenous populations, including the Quilombolos, a community descended from runaway enslaved peoples. The tailing ponds for bauxite mining impact indigenous fisheries and, according to some reports, are at risk of collapsing, which would completely destroy this way of life along the rivers.
While MRN has been mining bauxite in the Amazon Rainforest since the 1970’s the geologic origin of this material dates back much farther, to the very hot and humid climate of the late cretaceous period, 100 million years ago. The formation of Bauxite came through the weathering of sediment layers, slowly removing silica and other minerals from the soils, and leaving the alumina rich bauxite, the mineral which used to produce both for the Alumina Hydrate in the studio as well as most of the Aluminum in North America, the metal that we depend on for a wide range of technologies that are central to our modern lives.