This is technique using fuming(a technique of blowing heated gold or silver particles onto glass to create color),and the silver blue color is distincive
 
This product is made of heat-resistant and durable glass called borosilicate glass (Pyrex), which makes it extremely shatter-resistant and safe.
Please note that each item is handmade by a craftsman, so there may be slight differences in color, size, and pattern.
Therefore, it is a one-of-a-kind item.
The color and appearance will change greatly depending on the color of the clothes you wear, the color of the light it catches, and the angle from which you view it.