Slaked lime (calcium hydroxide) [Ca(OH)₂] 
Calcium hydroxide, Ca(OH)2, a white powder obtained by adding water to quicklime (the CaO formula refers to quicklime).
Characteristics
- Strong, fast-reacting base; caustic to skin, eyes and lungs.
- Source of calcium; raises the pH of solutions and soils.
- Approved in the EU as a basic substance (Implementing Regulation (EU) 2015/762).
- Traditional component of mineral broths in agroecological literature.
Role in the preparation: Acts as an alkalinizing agent and calcium source, and neutralizes acidic components in mineral broths.
Caution: Wear gloves, goggles and a dust mask, since contact causes chemical burns and inhaled dust injures the lungs; store closed and dry.
Sources: Oregon State University Extension – Applying hydrated lime to my garden? · EUR-Lex – Commission Implementing Regulation (EU) 2015/762 (calcium hydroxide, basic substance)
Documentary information: this is neither a recommendation for use nor a plant-protection or veterinary claim. Check your country's regulations before any use.