650ml Square Thick Glass Bourbon Whisky Bottle Decanter

Many bottles have a very thick glass bottom. What is this for and how is it made?

The thickening of the glass at the bottom of the bottle is done mainly for aesthetic reasons, to make the bottle look more valuable and to increase the transparency and purity of the bottle in the case of clear glass. Technically speaking, the glass concentration at the bottom of the bottle is achieved by creating a special preparatory mold (parison) with a higher quality of glass than normal bottles, which does not deform during the first blowing process.