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Material World
Material · Engineered

Porcelain

Clay, feldspar and quartz fired until they partly turn to glass — white, translucent, non-porous, and a Chinese secret for six hundred years.

Porcelain is the triaxial ceramic body: kaolin clay for plasticity, feldspar as a flux, and quartz as a filler, fired to around 1,300 °C. At that temperature the feldspar melts and the melt dissolves part of the quartz and clay, so the fired body is a glass with crystals suspended in it rather than a sintered powder.

That glassy phase is why porcelain is what it is: non-porous without needing a glaze, translucent in thin section, strong, and ringing when struck. Earthenware fired at lower temperature is porous and must be glazed to hold water.

History

China produced porcelain from roughly the seventh century and Europe could not reproduce it for another thousand years, which is one of the longer-standing technology gaps in history. Enormous effort went into imitating it — soft-paste porcelains made with glass frit, Medici porcelain, bone china with calcined bone ash — all of them approximations of a body whose ingredients were not known.

The problem was kaolin and temperature. European potters lacked both the right clay and kilns that could reach 1,300 °C, and the answer was found at Meissen in 1708 by Johann Friedrich Böttger, an alchemist imprisoned by Augustus the Strong to make gold and set to work on porcelain when that failed. The recipe was a state secret and leaked within a decade.

Uses

Tableware, sanitaryware, tile and figurines, and a large technical trade that most people never see: high-voltage insulators, laboratory ware, dental crowns and the substrates in electronics.

The electrical use is the one that mattered industrially. Porcelain's combination of high dielectric strength, weather resistance and mechanical strength made it the standard insulator for overhead power transmission, and the shapes on a pylon are porcelain doing a job no cheaper material did as well.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

is composed of

  • Clay — material · 40–60% · kaolin, for the plasticity that lets the body be shaped before firing
  • Feldspar — mineral · 20–30% · the flux: it melts at firing temperature and the melt dissolves part of the rest, which is what makes the body glassy and non-porous
  • Quartz — mineral · 20–30% · the filler that holds the shape while the feldspar is molten

is produced by

  • Firing — process · at around 1,300 °C — the temperature European potters could not reach, which is half the reason porcelain stayed a Chinese secret for a thousand years

is used as

  • Glass and ceramics — application · the demanding end of the trade, and the reason the industry buys feldspar at all
  • Structural engineering — application · as high-voltage insulators, where dielectric strength, weather resistance and mechanical strength are needed together and nothing cheaper does all three
  • Tableware and vessels — application · what displaced pewter, on weight, price and the lead question at once — and non-porous without a glaze, which earthenware is not

is an alternative to

  • Pewter — alloy · in tableware, and it won completely: industrially produced ceramics were lighter, easier to clean, did not dent, and by the nineteenth century cost less
  • Stoneware — material · both vitrified; porcelain is whiter, translucent and fired higher, and stoneware is tougher and more forgiving to make
  • Bone china — material · the English answer to a Chinese body Europe had failed to reproduce for a thousand years — arrived at from the wrong direction, by adding bone ash to a failing soft-paste recipe, and ending up stronger and more translucent than the thing it was imitating

is produced at

  • Jingdezhen — place · more or less continuously for over a thousand years, on local deposits of both kaolin and porcelain stone

is commonly confused with

  • Bone china — material · 'fine china' is used for both and means nothing; the working distinction is that bone china is warmer white, more translucent at the same thickness, and rings at a higher pitch

Sources

  • Material World
    Our own writing
  • Wikidata
    Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)

Questions this page answers

Where it comes from, and what it becomes

Follow Porcelain back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

  • Porcelain → is produced by (at around 1,300 °C — the temperature European potters could not reach, which is half the reason porcelain stayed a Chinese secret for a thousand years) → Firing → takes as input (to 1200–1300 °C, which is the vitrification that separates it from earthenware — and it is a temperature rather than a recipe) → Stoneware → is sourced from (a clay that survives 1200 °C and above, which an earthenware clay does not) → Clay → is sourced from (clay is chiefly what feldspar becomes when it weathers) → Orthoclase
  • Porcelain → is composed of (kaolin, for the plasticity that lets the body be shaped before firing) → Clay → is sourced from (clay is chiefly what feldspar becomes when it weathers) → Orthoclase
  • Porcelain → is composed of (the filler that holds the shape while the feldspar is molten) → Quartz
  • Porcelain → is composed of (the flux: it melts at firing temperature and the melt dissolves part of the rest, which is what makes the body glassy and non-porous) → Feldspar
  • Porcelain → is produced by (at around 1,300 °C — the temperature European potters could not reach, which is half the reason porcelain stayed a Chinese secret for a thousand years) → Firing → takes as input (to 1000–1150 °C, below vitrification, which is why it stays porous and why it was achievable before anybody could build a hotter kiln) → Earthenware → is sourced from (almost any clay, which is why it is the ceramic every early culture reached first) → Clay → is sourced from (clay is chiefly what feldspar becomes when it weathers) → Orthoclase
  • Porcelain → is produced by (at around 1,300 °C — the temperature European potters could not reach, which is half the reason porcelain stayed a Chinese secret for a thousand years) → Firing → takes as input (shaped and dried, then heated past the point where its minerals break down irreversibly) → Clay → is sourced from (clay is chiefly what feldspar becomes when it weathers) → Orthoclase

These are the most distinct paths back. Porcelain can be traced through others besides.

Downstream — what it becomes

  • Porcelain → is used as (the demanding end of the trade, and the reason the industry buys feldspar at all) → Glass and ceramics
  • Porcelain → is used as (as high-voltage insulators, where dielectric strength, weather resistance and mechanical strength are needed together and nothing cheaper does all three) → Structural engineering
  • Porcelain → is used as (what displaced pewter, on weight, price and the lead question at once — and non-porous without a glaze, which earthenware is not) → Tableware and vessels
  • Porcelain → is produced at (more or less continuously for over a thousand years, on local deposits of both kaolin and porcelain stone) → Jingdezhen