Hydroxide

Potassium hydroxide flakes

Lye is a corrosive alkaline substance, commonly sodium hydroxide (NaOH, also known as Caustic soda) or historically potassium hydroxide (KOH, from hydrated Potash). Previously, lye was among the many different alkali leached from hardwood ashes.

Potassium hydroxide is an inorganic compound with the formula KOH. Along with sodium hydroxide, this colorless solid is a prototypical "strong base". It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive nature.

Aluminium hydroxide, Al(OH)₃, Alum, is the most stable form of aluminium in normal conditions. It is found in nature as the mineral gibbsite (also known as hydrargillite) and its three, much more rare, polymorphs: bayerite, doyleite and nordstrandite.