✨ The Truth About Luster on Ceramics ✨ I often come across concerns about the safety of drinking from luster-glazed mugs, with some people mistakenly assuming they are toxic. However, these concerns stem from a lack of understanding of ceramic production techniques, and I’d like to clarify the facts. Luster is a thin metallic coating applied over a fully glazed and fired ceramic surface. It undergoes a 𝘁𝗵𝗶𝗿𝗱 𝗳𝗶𝗿𝗶𝗻𝗴 at approximately 700–800°C (1292–1472°F), where it bonds with the glaze, creating the iridescent, metallic sheen. The composition of luster varies, but it typically contains precious metals such as gold, platinum, or iridescent compounds that produce the shimmering effect. 𝗜𝘀 𝗹𝘂𝘀𝘁𝗲𝗿 𝗱𝗮𝗻𝗴𝗲𝗿𝗼𝘂𝘀? In its raw liquid form, yes. It contains volatile solvents and metallic compounds that can be harmful if inhaled or absorbed through the skin. When working with it, I always use gloves, a respirator, and ensure strong ventilation. Additionally, the kiln firing releases toxic fumes, making it unsafe to be in the same space during the process. However, 𝗼𝗻𝗰𝗲 𝘁𝗵𝗲 𝗽𝗶𝗲𝗰𝗲 𝗵𝗮𝘀 𝗯𝗲𝗲𝗻 𝗽𝗿𝗼𝗽𝗲𝗿𝗹𝘆 𝗳𝗶𝗿𝗲𝗱, the luster transforms into a stable, bonded surface. After cooling, I conduct a 𝗹𝗲𝗮𝗰𝗵 𝘁𝗲𝘀𝘁 to ensure that no harmful substances migrate from the ceramic surface. The test I use is the lemon test, which is a simple but effective way to detect whether any metals are leaching from the glaze. Citrus acids can accelerate metal leaching if the glaze is unstable, but my tests have shown zero leaching, confirming that these mugs are completely safe for use. Moreover, the 𝗶𝗻𝘀𝗶𝗱𝗲 𝗼𝗳 𝗺𝘆 𝗺𝘂𝗴𝘀 𝗶𝘀 𝗻𝗼𝘁 𝗰𝗼𝗮𝘁𝗲𝗱 𝘄𝗶𝘁𝗵 𝗹𝘂𝘀𝘁𝗲𝗿, only the exterior. This means that even in the unlikely event of any instability, it wouldn’t come into direct contact with beverages. So, next time you hear someone say that luster ceramics are unsafe, know that 𝗶𝘁’𝘀 𝘁𝗵𝗲 𝗿𝗮𝘄 𝗺𝗮𝘁𝗲𝗿𝗶𝗮𝗹 𝘁𝗵𝗮𝘁 𝗶𝘀 𝗵𝗮𝘇𝗮𝗿𝗱𝗼𝘂𝘀 𝗱𝘂𝗿𝗶𝗻𝗴 𝗽𝗿𝗼𝗱𝘂𝗰𝘁𝗶𝗼𝗻, 𝗻𝗼𝘁 𝘁𝗵𝗲 𝗳𝗶𝗻𝗶𝘀𝗵𝗲𝗱 𝗽𝗶𝗲𝗰𝗲. Through proper firing and testing, these mugs are not only beautiful but also safe for daily use.