Crucibles are to be considered consumable, and their lifetime is closely tied to their use and proper cleaning. The average lifetime is 20-30 analyses.
Crucibles have class 2 porosity according to Jena’s definition, with 45 µm (40 – 60 µm) (ASTM) holes, class C in the USA. In particular, the lifetime of crucibles is closely correlated with their proper use in the muffle furnace for analyzing ashes and their proper cleaning in keeping with what is
recommended in the operating manual.

The heating and cooling of glass crucibles for determining ash content require special care in order to keep them from breaking.
Both the heating and cooling of glass conducted at speeds that are too high induce tensions between the various parts that lead to breakage, particularly if close to grazes or in particularly stressed areas such as the junction between the crucible body and the filter disk. Bear in mind that the temperature of 550° corresponds to the beginning of glass’s plastic state, and therefore should not be exceeded.