This is a diving mask designed to see in water, and is called nun, or an eye, by female divers in Jeju Island. It was often used to dive into deep or heavily polluted water. In the past, people dived with their bare eyes, until the late 19th century, when flat glass was introduced and became the core material of diving goggles. This subsequently enabled the widespread use of diving masks and their adoption by the female divers of Jeju. With the introduction of the mask, divers were able to secure a greater field of vision than they did with bare eyes, and see more clearly in deep water. In addition, the diving mask was not commonly used until the early 20th century, when the growing scarcity of abalones and other shellfish required its usage for diving into deeper water. Wangnun, a single-lens diving mask, which resembles those used today, was first produced in the 1950s, and before that, a type of double-lens diving glasses called joksenun had been used. The diving mask shown here is generally worn tightly stuck to the wearer’s face when underwater. The lens on the front is made of glass, while the part touching the face is made of rubber. The connecting part between rubber and glass is reinforced and tightly secured using copper to prevent the glass from separating from the rubber. In addition, the rubber band designed to be tied around the head to secure the mask to the face is also attached to a rubber rim to be waterproof. The part that touches the face is designed to fit around the curves of the face.