316L stainless steel - also known as surgical steel - is used for the overwhelming majority of modern wristwatches. 904L Stainless steel - from which Aera watches are made - is known as a superalloy. 904L has more nickel, chromium, molybdenum, and copper which makes it more expensive and harder to process. However, it is more resistant to corrosion and pitting, which means a longer life for the case and a more durable finish, which is why it is used in the aerospace and chemical industries. Increased chromium content also gives the brushed surface a deeper, more lasting lustre whether polished or brushed. Yet it is still surprisingly rare in watchmaking. So, it is for both practical and aesthetic reasons we decided to go the extra mile.