Titanium alloy is currently known as the hardest material for making eyeglasses. It avoids the defect that pure titanium is easy to break. It has ductility and toughness. It can make the thinnest reading glasses, and of course it can also make the lightest metal glasses. Besides its light weight, the biggest advantage is that it is an inert metal, so it won't be corroded without any coating. Gold plating has the strongest adhesion, followed by silver and gunmetal. Black is usually a spray paint, so you know it will fade after about 3 years.