The refining of crystal/handmade glass is often achieved by using a redox-reduction where arsenic &/or antimony oxide are oxidised by nitrate. The trivalent metal is oxidised to the pentavalent state. The equilibrium between the two different oxidation states can be described according to the following equation. M2O3+O2M2O5 where M=As or Sb. At higher temperatures the reaction is shifted to the right & oxygen will be released into the melt. The efficiency of arsenic & antimony has been compared in earlier studies. When comparing arsenic (III) oxide, antimony (III) oxide & mixes between the two, refining with antimony alone is most efficient in the studied lead glass. There is an almost 10-fold improvement with antimony (III) oxide as refining agent. Arsenic is more toxic than antimony & as there is no improvement by arsenic additions antimony refinement is to be recommended.
