Our thermo glass (also known as borosilicate glass ) products undergo a meticulous hand-finishing and polish process, including handle attachment and firing in small batches, highlighting the craftsmanship involved in their creation. While we maintain stringent quality control, it's important to note that approximately 1% of the goods may exhibit minor imperfections such as small air bubbles due to the artisanal nature of production. Although we make diligent efforts to filter out such items, there is a rare chance that these subtle nuances may be present in some shipments. We appreciate your understanding of the inherent uniqueness of handcrafted goods and remain dedicated to delivering exceptional quality across our product range.