• Hydrated alumino-silicate weathered from feldspars
• (Si₂O₅) layer of SiO₄^2- tetrahedrons joined at corners
• AlO(OH)₂ layer of octahedral arrangement of O and OH around the Al
• Layers connected by O^2- ions which are shared by the layers
• Substitutions of Mg²⁺ for Al³⁺ in the AlO(OH) layer gives the layer an overall negative charge.
• Charges balanced by cations that insert between layers: Ca²⁺, K⁺, Na⁺

• Ball clay: high plasticity, good dry strength. Needs temper. Name from practice of digging balls of clay from open pits (20-30 pounds, to carry). Cream colored after firing. Vitrify at 1100-1200 C.
• China clay: moderate plasticity (less than ball clay or montmorillonite), fires white. Primarily kaolinite (mine in China: Kaoling)
• Montmorillonite: good plasticity and high drying shrinkage from small particle size. High alkali.

• Typical: 50% clay + 50% non-plastic
• Balance plasticity and drying behavior
• Hard porcelain: 25% ball clay (fine particle size, high plasticity) + 25% china clay (larger particle size, less plasticity) + 25% feldspar + 25% flint
• Soft-paste porcelain (fine particle size, highly plastic limey (CaO) clay) 10-15% clay (montmorillonites)

1. Permeable earthenware
2. White quartz-paste bodies
3. Vitreous stoneware
4. White porcelain

• Good plasticity
• Archaeologically prevalent going back 10,000 years
• High in iron, lime, soda, potassia, impurities
• Can fire as low as 700 Celsius
• Material:
• Clay
• Non-plastic minerals
• Sandy materials decrease drying shrinkage, making joining easier; also makes shaping easier
• Limestone or shell temper increases workability through increased alkali
• High lime clays, or clays with high quartz content contract more on cooling, so glazes are less likely to craze or spall. Red clays have lower thermal expansion and contraction than lime clays.
• Iron oxide
• Color control understood as early as 6000 BC
• Oxidized form: Fe₂O₃ has 1.5 oxygen/iron atoms (red)
• Reduced form Fe₃O₄ has 1.33 (black)
• Red-on-black:
• Fine particle size, alkaline-rich iron-containing clay as slip
• Fire in reduction, and slip vitrifies to black, with grey body
• Kiln opened, cool in oxidation, allowing body interior to oxidize, forming a red body, while the impermeable slip decoration remained black.

Egyptian faience,

Islamic quartz-clay-frit ware

• Quartz crushed from pebbles is pure and white
• Quartz contraction on cooling is large (2%), resulting in good compatibility with alkaline glazes
• Faience
• White Islamic wares (predate European porcelain)
• Quartz
• Pre-melted glass frit
• Plastic white clay

Quartz-clay-feldspar

Bottger red ware (clay-gypsum)

• By end of Shang Dynasty (1000 BC), kiln temperatures were 1200 Celsius
• Proto-porcelain: iron oxide-containing clay-mica-feldspar-quartz mineral raw material fired to strong gray stoneware. Lowered iron content and higher kiln temperatures
• 1708 Bottger introduces stoneware from red clay and limey clay.
• Fine mullite crystals in an alkaline silicate glass form microstructure

• By end of Han Dynasty (221 BC — 220 AD), kiln temperatures were 1300 Celsius
• Allow dense vitreous body with low iron (less than 1%)
• China stone, quartz, mica, feldspar and kaolin
• Bottger used clay-gypsum with low iron to make white porcelain
• Later, use feldspar in addition to lime or gypsum.
• Fine mullite crystals in an alkaline glaze associated with quartz.
• Medici differed: alkali-silicate sintered together with quartz and white clay.
• Soft-paste porcelain improved this, using alkali-silicate sinter with a lower clay content and lime. Cristobalite grains and fine wollastonite crystals in an alkaline glass matrix.
• English bone china: bone ash (calcium phosphate) and feldspar with clay and quartz

• Beleek porcelain: melted frit and feldspar with clay and quartz