An hourglass, also known as a sand clock, is a device used for measuring time.

An hourglass consists of two glass bulbs connected by a narrow passage through which sand flows from one bulb to the other.

Typically, a certain amount of fine sand is contained inside, and the time is measured as the sand gradually flows from one bulb to the other. Inverting the hourglass allows for continuous-time measurement. The duration of time measured depends on the amount of sand and the size of the passage.

History of Hourglass

The hourglass is said to have originated in the 12th century for nighttime navigation, as time could be calculated during the day by observing the sun but not at night.

The earliest recorded mention of the hourglass was found in a mural dating back to 1338 in Italy.

By the 15th century, hourglasses began to be widely used and were available in the market, primarily for maritime navigation, industrial, and culinary purposes.

Manufacturing Process of Hourglass

The process begins with the selection of sand. Natural sand, due to its irregular shape and lack of smoothness, is unsuitable for hourglass making. Nowadays, hourglasses commonly use micro-glass beads. For highly accurate timing hourglasses, a desiccant called silica is used.

The sand is heated in a pot to evaporate excess moisture, leaving only 20% moisture content to prevent it from sticking to the glass walls.

Glass tubes are cut into the desired size for the hourglass. Each cut glass tube serves as the prototype for an hourglass.

The hourglass shape is formed by processing the glass at high temperatures. Initially, low temperatures are used to heat the glass tube, which is then stretched from both ends to create a narrow passage in the middle. The size of the passage relies on the experience of the worker.

The bottom of the hourglass is made to allow the glass to stand upright. The end of the glass tube is heated and pinched with small pliers while rotating until a bottleneck is formed, and then the end is sealed.

The top and bottom parts of the hourglass are circular glass bulbs, formed by heating the glass to a high temperature and manually blowing and shaping it.

The glass tube with sand is sealed at one end, adjusting the amount of sand to measure time accurately, and repeating the process multiple times to achieve the correct amount of sand.

The other end of the glass tube with sand is sealed, forming a bottleneck and sealing it using high temperature and pliers.

A complete hourglass is now finished.

Hourglass symbolizes the passage of time, representing the finite nature of life and the inevitability of death. It emphasizes the continuous and one-way flow of moments, serving as a poignant reminder of the brevity of human experience.

The flowing sand symbolizes the ticking of moments, encapsulating the transient quality of life and the importance of living in the present. In a broader sense, the hourglass can also symbolize the balance and cyclical nature of the world, as the sand perpetually moves from one chamber to another.