Rare and unusual metal oxides in Crystalline glazes
To further both my understanding and the collective knowledge of ceramics I procured and tested 7 rare earth oxide colorants in 4 different crystalline glazes. Isolating 4 compositions for the 4 main crystal glaze types: Zinc, Zinc Free, Aventurine, and Molybdenum, I proceeded to add 7% by weight of each colorant to the glaze base. The oxides used are as follows: Erbium, Cerium, Lanthanum, Neodymium, Europium, Praseodymium, and Holmium. These tests were then fired in a specialty cone 6 electric firing to achieve peak crystal development. Neodymium and Holmium were chosen for their known ability to change color depending on the type of light it is being viewed under. Similarly, Europium was chosen for its reactivity to ultraviolet light. Erbium and Praseodymium were chosen for their ability to impart transparent pink and green respectively. The Lanthanum and Cerium were chosen for experimental purpose, as their effects in glaze have not been widely studied. The 7% addition of each oxide provided enough chromophore to alter each glaze, but the percentage could absolutely be increased for different or more intense effects. Overall, these oxides each impart a glaze effect that is either very difficult or impossible to archive with only common metal oxides.
After studying how crystal firings effects the appearance of the glaze, I selected the Nick Ramos Cone 6 Crystal firing schedule. I found this cycle has a good balance between peak holds and temperature drops to maximize the crystalline development in all my glazes. This schedule was found on Nick Ramos’s Glazy page, as shown below.
Oxides in raw states:
Top row: Erbium, Cerium, Lanthanum, Neodymium
Bottom row: Europium, Praseodymium, Holmium
The first hurdle was finding a stable glaze of each crystal type that fully vitrified at cone 6 and could crystalize in the same firing. After researching these glaze types and pulling 21 glaze recipes from books, academic papers and the website Glazy.com, I began to mix and test each one with 2% by weight of copper to see the each glazes response to a metallic coloring agent. Each glaze was tested on porcelain with one side brushed and one side dipped. This difference in application made a massive difference on crystal formation across all glazes. For detailed Analyses a specific glazes, Please contact me at aspenologii@gmail.com with the name of the glaze you would like.
Zinc
Left to Right:
CSMCG 7, CSMCG 8, Farley Macrocrystalline, Nick Ramos Crystal, Crystal JH, Zinc Bloom
Left to Right:
CSMCG 7, CSMCG 8, Farley Macrocrystalline, Nick Ramos Crystal, Crystal JH, Zinc Bloom
“D” Tiles: Dipped (2 Seconds long, 1 coat)
“B” tiles: Bushed (2-3 coats)
Zinc Free
Left to Right:
Tilton 1, Seasalt, Pam’s Crystalline Matte, Nelson Crystal, Wolly Fruit
Left to Right:
Tilton 1, Seasalt, Pam’s Crystalline Matte, Nelson Crystal, Wolly Fruit
“D” Tiles: Dipped (2 Seconds long, 1 coat)
“B” tiles: Bushed (2-3 coats)
Aventurine
Left to Right:
MP Aventurine, C6 OR1, Snair Goldstone, CSAG 5, Baby Funko Sparkle
Left to Right:
MP Aventurine, C6 OR1, Snair Goldstone, CSAG 5, Baby Funko Sparkle
“D” Tiles: Dipped (2 Seconds long, 1 coat)
“B” tiles: Bushed (2-3 coats)
Molybdenum
Left to Right:
MA #1, MA#2, MA#4, Herbert Sanders Molybdic, Bassets Moly
Left to Right:
MA #1, MA#2, MA#4, Herbert Sanders Molybdic, Bassets Moly
“D” Tiles: Dipped (2 Seconds long, 1 coat)
“B” tiles: Bushed (2-3 coats)
After carefully contemplating the visual aesthetics, the amount of running ,and how the glazes performed with the added colorant I chose the 4 glazes i would move forward with. Nick Ramos Crystalline had the classic zinc crystal patterns that i was after and stayed contained on the test tile even though it ran. Wolly Fruit was selected for its superior crystallization and for its breakage over the edge of the tile. Mp Aventurine exhibited the most aventurine crystals across the 5 tests and was selected even though the copper carbonate did not effect it much. MA#1 was selected for its stability, color response, maximal molybdenum crystal growth, and ease of access to materials. After selecting these I mixed dry batches of each and separated them into 8 cups, 1 for a control and 7 for the oxide colorants. The colorants are Erbium, Cerium, Lanthanum, Neodymium, Europium, Praseodymium, Holmium in their respective oxide forms. I decided to go with 7% Rare Earth Oxide (REO) Per weight. This is the standard amount i have found across recipes published on Glazy and in discussion with my Professor. Each tile was dipped in the glaze and fired in the same cycle as the preliminary tests.
Zinc
Dipped (2 Seconds long, 1 coat)
L-R
Base, Erbium, Cerium, Lanthanum, Neodymium, Europium, Praseodymium, Holmium
Zinc Free
Dipped (2 Seconds long, 1 coat)
L-R
Base, Erbium, Cerium, Lanthanum, Neodymium, Europium, Praseodymium, Holmium
Aventurine
Dipped (2 Seconds long, 1 coat)
L-R
Base, Erbium, Cerium, Lanthanum, Neodymium, Europium, Praseodymium, Holmium
Molybdenum
Dipped (2 Seconds long, 1 coat)
L-R
Base, Erbium, Cerium, Lanthanum, Neodymium, Europium, Praseodymium, Holmium
Some of these oxides were chosen for their special reactivity with certain lights. The oxides Holmium and Neodymium are visually different colors depending on the light source. Neodymium appears to be a soft baby blue under fluorescent lights and shifts to a similarly hued amethyst purple under natural sunlight. Holmium appears to be be a bright pink under fluorescent light, but shifts to a honey colored tan-yellow when exposed to sunlight. Europium under any common light )flourscent, daylight, etc) remains ivory colored, but once its exposed to direct Ultraviolet light it glows bright orange-reddish.
Left to Right:
Nick Ramos Crystalline, Wolly Fruit, MP Aventurine, MA#1
Left to Right:
Nick Ramos Crystalline, Wolly Fruit, MP Aventurine, MA#1
Left:
Neodymium tiles under fluorescent lights
Right:
Neodymium tiles under natural daylight
Left to Right:
Nick Ramos Crystalline, Wolly Fruit, MP Aventurine, MA#1
Left to Right:
Nick Ramos Crystalline, Wolly Fruit, MP Aventurine, MA#1
Left:
Holmium tiles under fluorescent lights
Right:
Holmium tiles under natural daylight
Left to Right:
Nick Ramos Crystalline, Wolly Fruit, MP Aventurine, MA#1
Europium tiles under 365nm Ultraviolet light
In Conclusion, Rare Earth oxides can be used effectively across a broad range of crystalline glazes. these oxides overall do not change the efficacy of the crystallization process visually speaking. These oxides impart effects that are very difficult or near impossible to achieve with common metal oxides. If you would like to see these glazes in use, check out my piece called Fazes.