Phosphorous Pentoxide - P2O5

Amphoteric Unit 6 Topic 12
Oxide Qualities

Colloidal blues - opacifies with suspended small gas bubbles - sourced from ash.


  • Although technically an amphoteric P2O5 acts more as a glass-forming oxide though not a substitute for silica.
  • Present as a trace element in some materials.
  • Small amounts give colloidal opacity e.g. chun glazes.
  • Creates a matrix of small bubbles in a glaze giving light dispersal particularly pleasant in celedons.
  • Shows as a bluish flush in a glaze.
  • Large amounts give opacity, a dull surface, and blistering.

Insoluble Sources

  • Vegetable ashes - small amounts occur in these.
  • Bone ash Ca3(PO4)2 - the most common controllable source. Also brings calcia.
  • Amblygonite Li.AlF.PO4 - also brings lithium oxide and alumina.

Soluble Sources

  • Fertilisers - superphosphate derived from phosphorite rocks.
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