tuhk

Tuhk is the word used in Finnish and Estonian to denote ash, the powdery residue left after combustion. It forms when organic materials such as wood, coal, or other fuels burn, leaving inorganic mineral components behind. In everyday contexts, tuhk can refer to both natural volcanic ash and man-made ashes from combustion.

There are several main types of tuhk by source. Wood ash results from burning biomass in stoves or fireplaces and is typically alkaline, containing calcium carbonate, potassium carbonate, and trace minerals. It can raise soil pH and supply nutrients but should be used carefully to avoid imbalances. Coal ash is produced from burning coal and includes fly ash (fine particles captured from exhaust) and bottom ash (coarser residue). Fly ash is often used as a pozzolanic additive in cement and concrete, as well as in some geotechnical applications, but it can contain trace metals and requires proper handling and disposal. Volcanic ash, or tephra, is emitted during explosive eruptions and consists of fine glassy and crystalline particles; it can affect air quality, aviation, and landscapes, forming layered deposits on the ground.

Composition and properties of tuhk vary by source. Wood ash is rich in calcium and potassium compounds; volcanic ash is primarily silica-rich and abrasive; coal ash contains a mix of oxides including silicon, aluminum, calcium, and trace metals. The health and environmental impacts depend on particle size and chemical content: inhalation of fine ash can irritate the respiratory system, and silica-bearing ash poses specific health risks.

Uses of tuhk include soil amendment, where appropriate, and industrial applications such as cement admixtures, in addition to historical uses like soap making with ash-derived lyes.