Idea of Historical Icon
This is a picture of an hourglass. It has more sand in the bottom than the top, and it's top and bottom parts are squarely shaped, almost like a crown moulding. It is symmetrical besides the amount of sand.
This Historical icon is made in Material Design style
developed by Google. This style is based on extremely simplified shapes, thin two-pixel lines, and is optimized for 24x24 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 6,100 icons, all in the same style and quality.