Made of top quality 3.3 borosilicate glass. Maximum temperature: 220 ºC (heat and cool in a slow and controlled manner). Each crucible has a sintered disc with a different porosity grade: 150 – 200 μm (porosity 0), 90 – 150 μm (porosity 1), 40 – 90 μm (porosity 2), 15 – 40 μm (porosity 3), 5 – 15 μm (porosity 4), 1 – 2 μm (porosity 5)