Arsenic

A highly toxic semi-metal (As), recovered in Cornwall almost entirely as a by-product of roasting tin and copper ore, and refined for use as a pesticide, pigment and industrial chemical.

Historical usage

Arsenic occurs naturally alongside Cornish and Devon tin and copper ores, chiefly as the mineral arsenopyrite, and was originally just a contaminant vented to the atmosphere while roasting ore for its tin. Once markets for arsenic itself — pigments, pesticides, glass decolourising — developed in the early 1800s, mines began recovering it deliberately in purpose-built calciners. By the 1870s a handful of Cornish and Devon mines produced over half the world's arsenic; Devon Great Consols alone, the largest producer, refined some 3,000 tons of arsenic a year at its peak.

How it worked

Arsenopyrite-bearing ore was roasted at around 600°C in a Brunton calciner, driving off arsenic and sulphur as gas along with the tin being recovered; the gases were drawn through long, winding flues and arched condensing chambers, where the cooling arsenic deposited as a grey-white crust of refined arsenic trioxide on the chamber walls, later scraped out, re-refined and packed for sale.

Why it was used

Arsenic's toxicity was exactly what made it commercially valuable — as a pesticide, rat poison and sheep-dip it killed pests reliably and cheaply, while its use as a glass decolouriser and pigment depended on unrelated chemical properties; Lancashire's cotton industry, using arsenic-based dyes and pigments, was Cornwall's principal customer.

Value over time

Arsenic was, in effect, a waste stream that Victorian industry turned into one of Cornwall's most valuable exports: worthless contamination before the 1800s, it became profitable enough that Devon Great Consols could refine 3,000 tons a year by the industry's peak. That value collapsed just as quickly once its principal use — agricultural and household pesticides — was progressively restricted through the 20th century on safety grounds, and Cornish arsenic production was effectively phased out by the early 1900s as tin mining itself also declined.

Hazards & challenges

Arsenic is acutely and cumulatively toxic, and Cornwall's calciner workers — often women and girls tending the Brunton calciners — worked with minimal protection, sometimes no more than cotton wool wads in the nostrils and a cloth over the mouth against the arsenic-laden fumes and dust. The legacy is still measurable today: soil around former calciner sites in Cornwall records some of the highest arsenic concentrations found anywhere in the world, up to around 2,500 parts per million, a direct record of just how much toxic material passed through these sites and how little of it was contained.

Risks & limitations

Because arsenic was almost always a by-product rather than a mine's primary target, its production tracked the fortunes of the tin and copper industry that generated it rather than following an independent market of its own — when Cornish tin mining declined, arsenic output declined with it regardless of arsenic's own market conditions.

Regional variation

Cornwall and west Devon were overwhelmingly the centre of British arsenic production, a direct consequence of the region's tin and copper lodes running through arsenopyrite-bearing rock; arsenic recovery on this scale was not significant anywhere else in Britain.

Images

Mines associated with this term

Included only where MineArchive's own research gives a reasonable evidential basis — not every mine where this might plausibly apply.

• Botallack Mine — Cornwall (well documented example)
  Its cliff-top arsenic refining works and calciner flues are among the site's most recognisable surviving structures.
• Consolidated Mines — Cornwall (well documented example)
  Part of the Gwennap mining district at the heart of Cornwall's arsenic industry.
• Devon Great Consols — Devon (well documented example)
  The largest arsenic producer in the world at its peak, refining around 3,000 tons of arsenic a year.
• Dolcoath Mine — Cornwall (well documented example)
  A major Cornish mine that recovered arsenic as a by-product of its tin and copper working.
• East Pool Mine — Cornwall (well documented example)
  Recovered arsenic alongside its main tin and copper production.
• Wheal Jane — Cornwall (well documented example)
  Recovered arsenic as a by-product; its 1992 discharge — see this site's own account — was itself partly an arsenic-contaminated event.

Sources

1. (primary) Geochemical assessment of arsenic toxicity in mine site along the proposed Mineral Tramway Project, Camborne, Cornwall — Geochemistry: Exploration, Environment, Analysis
2. (secondary) 12: Minor Metals — 12.1 Arsenic — National Association of Mining History Organisations
3. (secondary) Extracting Arsenic — Cornish Mining World Heritage Site
4. (secondary) Poison Panic & the History of Arsenic — Historic UK

Record created: 20 August 2026 · Last researched: 20 August 2026