*Although platinum’s unusual properties make it ideal for laboratory ware, there are some elements that attack it… particularly at high temperatures. Examples are: Lead, tin, zinc, bismuth, arsenic, anatomy, phosphorous, selenium and tellurium.
The regular cleaning and burnishing of platinum ware will prolong the life of crucibles and dishes. Immersion in the commonly employed chromic acid cleaning mixture will remove many impurities, particularly organic matter. Boiling in hydrochloric acid may be required to remove insoluble carbonates or metal oxides. Boiling in nitric acid may follow this treatment, but care should be taken to first rinse the article thoroughly since the presence of hydrochloric acid in the nitric acid solution would result in an attack upon the platinum. The solvent action of fused potassium bisulfate may usually be relied upon to remove adherent silica, silicates, metals and metal oxides. After fusion, carefully run the molten bisulfate over the inner surface, allow to cool, dissolve the melt in boiling water and rinse thoroughly. Boiling in hydrochloric acid may be required to supplement this procedure. After cleaning, the platinum crucible or dish may be polished by gently rubbing with an alumina impregnated nylon webbing having a fine grit.
Platinum is a relatively soft metal and it is not surprising, therefore, that inadvertent mishandling of laboratory apparatus will produce dents or other distortions. Using a reshaping block and plug may reshape crucibles.
**The life of crucibles and dishes can be prolonged through the regular use of re-shapers to smooth out dents and distortions.