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Material World
Application

Pigment

Insoluble particles that give a material colour by absorbing part of the spectrum.

A pigment colours by remaining as discrete particles that absorb some wavelengths and scatter the rest, which is what distinguishes it from a dye that dissolves. That difference makes pigments far more durable, and it is why the oldest surviving human images are pigment.

The practical requirements are demanding: a pigment must be intensely coloured, insoluble, stable to light and heat, and not react with whatever it is mixed into. Historically most were mineral, and several of the best were poisonous.

Medium confidence Weak evidence 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.

uses

  • Hematite — mineral · as red ochre
  • Cadmium — element · cadmium yellows and reds, now largely withdrawn on toxicity grounds
  • Cobalt — element · cobalt blue, in use for three thousand years
  • Lead — element · white lead and chrome yellow, both withdrawn
  • Selenium — element · selenium reds in glass and ceramic glaze
  • Strontium — element
  • Titanium — element · as titanium dioxide, which consumes more titanium by tonnage than metal production does
  • Magnetite — mineral · as a black iron oxide pigment, and historically in inks
  • Calcite — mineral · ground calcite is the white filler and extender in most paint
  • Aragonite — mineral · ground shell and aragonite as a white filler, and as the nacre used in inlay
  • Carnelian — mineral variety · not as a pigment — recorded because the iron oxide that colours it is the same compound used as one, at a different scale
  • Chalk — rock · as whiting — ground and washed chalk, used as an extender in paint, a filler in paper and PVC, and the mild abrasive in toothpaste
  • Charcoal — material · as vine and willow charcoal, and as the black in the oldest paintings there are — Lascaux and Chauvet are drawn in it

Sources

  • Material World
    Our own writing

Questions this page answers

Where it comes from, and what it becomes

Follow Pigment 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

  • Pigment → uses (cobalt blue, in use for three thousand years) → Cobalt → is sourced from (much of world supply arrives as a by-product of copper mining rather than from cobalt-first operations) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation
  • Pigment → uses (selenium reds in glass and ceramic glaze) → Selenium → is sourced from (from copper anode slimes, alongside the tellurium it accompanies and closely resembles) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation
  • Pigment → uses → Strontium → is produced by (the same aluminothermic route as barium, and in similarly small quantity) → Metallothermic reduction → takes as input (the cheapest reducing metal and the commonest, and the aluminium in thermite) → Aluminium → is extracted from (via alumina — bauxite is refined by the Bayer process before smelting) → Bauxite → is sourced from (the residue of prolonged tropical weathering, which strips the silica and alkalis out of an aluminosilicate rock and leaves the aluminium behind — basalt is one common parent among several) → Basalt
  • Pigment → uses (as titanium dioxide, which consumes more titanium by tonnage than metal production does) → Titanium → is produced by (as sponge, which must then be crushed, melted and cast before it is usable metal) → Kroll process → takes as input (the inert atmosphere, without which the titanium would take oxygen from the air) → Argon → is produced by (drawn from an intermediate height in the column, between nitrogen and oxygen) → Air separation → takes as input (the feedstock, and an unusual one in being free, unlimited and available anywhere — the cost is entirely the energy to liquefy it) → Air
  • Pigment → uses (as vine and willow charcoal, and as the black in the oldest paintings there are — Lascaux and Chauvet are drawn in it) → Charcoal → is produced by (the kiln burns a small fraction of the wood to supply the heat that pyrolyses the rest) → Pyrolysis → takes as input (to make coke, and the coal gas that came off it lit European cities for a century as the by-product) → Coal → is sourced from (every coal seam in the world was a peat bog. Bury it, compress it, heat it, and it passes through lignite and bituminous coal to anthracite, losing water and volatiles at each step) → Peat → is sourced from (waterlogging is the whole mechanism: a bog is anoxic below a few centimetres, so the organisms that would decompose the plant matter cannot work, and it accumulates instead) → Water
  • Pigment → uses (cadmium yellows and reds, now largely withdrawn on toxicity grounds) → Cadmium → is sourced from (cadmium substitutes for zinc in sphalerite and follows it through roasting; there is no cadmium ore and never has been) → Zinc → is produced by (as the oxide, which is then reduced — roasting is the step that makes zinc sulfide smeltable) → Roasting → takes as input (a copper sulfide; roasting drives off the sulfur that would otherwise prevent reduction) → Chalcopyrite

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