Ceramics I
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- What is the purpose of flux in glazes?
- Flux allows glassformers to melt, and influences surface texture and color.
- What are some glassformers listed as ingredients in our glazes?
- Silica (Si02/Flint) and Boron as bases, Arsenic and Phosphorus as additives.
- What is used as a stabilizer in our glazes?
- Alumina (Al2 03)
- What does a stabilizer do in a glaze?
- Stabilizers affect the mixture's viscosity.
- What is viscosity?
- The tendency of a liquid to resist flow.
- What are some fluxes found in glazes?
- Feldspar, Fritt, Talc (Mg CO3), Whiting (C2 C03), Dolomite (Mg Ca CO3), Wolastonite (C2 Si O2)
- Fritt does what as a flux?
- Fritt makes ingredients less soluble and makes toxic materials like lead safer to use.
- Talc, Whiting, Dolomite, and Wolastonite contain natural fluxes, such as?
- sodium, potassium, calcium, magnesium, barium, lithium, zinc, strontium, lead
- Some colorants in glazes are...
- iron (many colors, brown), chrome (green), copper (green), cobalt (blue), manganese (grey-brown), nickel (grey-brown), vanadium (yellow),uranium
- What are some influences on the color of glazes?
- percentage of colorant to other ingredients, atmosphere in the kiln, temperature fired, flux
- What is reduction?
- a reduction in the amount of oxygen in the kiln- physically alters glaze, coloring, etc.
- What are some opacifiers and what do they do?
- Tin, zirconium, and titanium all make glazes white and opaque.
- What kind of glaze did we use on stoneware projects?
- cone 9- high temperature
- What 4 categories of ingredients make up a glaze?
- glassformer, stabilizer, flux, colorant
- What is clay made of?
- decomposed igneous rock
- What is primary source clay?
- it is found near the rock it came from, and is thus coarser and more pure.
- What is secondary source clay?
- found far from its source, this clay is broken into fine particles. has lots of impurities.
- what is the shape of a clay particle?
- clay particles are flat hexagonal shapes that slide against eachother. they are in clumps in coarser clay.
- How does clay become more plastic?
- natural agents like mold and bacteria break down clay and make it aged and plastic. water forms a slippery film between plates.
- criteria to choose clay by include...
- color, temperature required, plasticity
- pure clay is what color?
- white!
- what is the chemical formula of pure clay?
- Al2 O3 2S1 O2 2H20 (or, alumina-silica-water)
- the clay we use is made of what 3 categories of ingredients?
- Clay (duh), filler, and flux
- What are some clay types, in order of higher temps/coarser to lower temps/finer?
- Kaolin, fire clay, stoneware, call clay, earthenware, bentonite
- what are some fillers in clay?
- grog, sand, flint
- what are some fluxes in clay?
- feldspar, talc, fritt
- what is meant by "vitreous"?
- water-tight, having a hard, glassy surface
- what is meant by "refractory?"
- material that can withstand high heat, like clay!
- What is grog?
- ground up fired clay
- what do fillers do?
- adds strength, reduces shrinkage, adds hard, non-plastic particles.
- about feldspar:
- for high temps, a natural decomposed igneous rock.
- about talc:
- magnesium silicate, in earthenware
- about fritt:
- man made. carefully chosen ingredients to control necessary temperature. ground up glassy material.
- When/where/what were the earliest known glazes?
- c. 5000 BC, in Mesopotamia and Egypt- Sodash and Borax (water soluble). Egypt had a turquoise paste.
- Early firing was done in_______. What problems did this cause? why?
- pitfires. made unstable, pourous pieces, due to lack of high temp
- following pitfires, ceramicists invented an_________ system for more durable pieces
- updraft/bank
- after updraft firing came_______. when/where?
- downdraft kiln. Hunn dynasty in china, 200 BC. used wood ash, limestone, feldspar as glazes.
- about porcelain:
- kaolin, feldspar, limestone. originated in china.