Glass, method for producing a glass, and glass melting apparatus

A method for producing a glass element made of borosilicate glass comprising the steps:

• i) providing a batch, comprising, in wt %:
• SiO2 60 to 90%;
• B2O3 0 to 20%;
• Al2O3 0 to 20%;
• Li2O 0 to 10%;
• Na2O 0 to 10%;
• K2O 0 to 10%;
• MgO 0 to 10%;
• CaO 0 to 10%;
• SrO 0 to 10%;
• and
• BaO 0 to 10%;
• ii) heating the batch to form a glass melt,
• iii) conditioning the glass melt, and
• iv) cooling the glass melt to provide the glass element, wherein, during step ii) and/or iii):
• a) the glass melt is heated at least in part with an electric resistance heater by subjecting electrodes to a heating current, wherein the heating current is an alternating current with a frequency from 1 kHz and 200 kHz is used;
• b) a contact surface with which the glass melt is in contact comprises 30% or more contact material in the form of melt-cast zirconium oxide material with a proportion of over 70 wt % ZrO2;
• and
• c) from 1% to 50% of a volumetric flow is withdrawn from a bottom material of the glass melt in a bottom region of the glass melt,
• wherein the glass element has, per kg of glass, 50 inclusions or fewer having a size from 2 μm to 10 μm,
• wherein the inclusions comprise gaseous inclusions, solid metallic inclusions, and solid nonmetallic inclusions.