Prince Rupert’s drops are glass objects (drops) with unique properties that have kept scientists captivated for centuries. These teardrop shaped structures, named after Prince Rupert of the Rhine who introduced them to Europe in the 17th century, exhibit extraordinary strength and fragility simultaneously.

The Rupert drops are formed through the rapid cooling of melted glass in water or some other liquid forming teardrop shapes that exhibit extraordinary strength in their heads yet extreme fragility in their long and delicate tails.

Prince Rupert's drop complete

The tails of these drops are extremely fragile and can easily break with minimal force. Their heads are strong, however, if damaged (hit by a hammer), they can disintegrate with an explosion.

Disintegrated Prince Rupert's drop

Preparation Techniques

The formation of Prince Rupert’s drops begins by dropping molten glass into cold water, creating a rapid cooling process known as quenching. This technique leads to the creation of a teardrop-shaped object with a long tail.

The head of the drop, which is the thicker end, can withstand a substantial external force, while the tail, often thinner than human hair, is extremely fragile and can shatter into tiny pieces upon even slight damage.

Safety Precautions

While preparing Prince Rupert’s drops, one must heat glass until it becomes molten and then carefully drop it into cold water. Caution must always be exercised throughout this process, as the sudden temperature change can cause the glass to shatter or result in thermal burns. 

Safety goggles and protective gloves should also be worn to prevent injuries from explosive fragmentation.

Alterations in Formation Process

The behavior of Prince Rupert’s drops is influenced by various conditions, including the cooling rate during their formation.

1. By altering the quenching process, different shapes and properties can be achieved. For instance, when the glass is cooled more slowly, the drops become more resilient, as the tension is gradually released during damage.

2. The chemical composition of the glass can also impact the strength and properties of the drops.

3. The nature of these drops may also be affected by the liquid in which the molten glass is cooled. Water creates the most ideal type of drops, because of its high heat capacity and less surface tension.

4. Honey, peanut oil, and other viscous liquids will therefore create drops with different properties i.e., more resilient to shattering.

Intriguing Properties

Prince Rupert’s drops possess intriguing mechanical properties due to their unique internal structure. The rapid cooling creates immense compressive stress on the outer surface of the drop, while the interior remains in a state of tension. 

This results in a unique distribution of forces that enables the drop’s head to resist hammer blows or compression forces, often withstanding even bullet impacts. However, if the tail is damaged, the internal tension is released, leading to the complete fragmentation of the drop.

Application of Prince Rupert’s Drops

Practically, Prince Rupert’s drops can be used in various fields.

1. They can be used as decorative items, jewelry, or even in specialized applications such as pressure sensors and optics.2. Their ability to withstand high impacts without shattering completely makes them a subject of interest in industries exploring durable and impact-resistant materials.3. Their impact resistance makes these drops plausible for protective eyewear such as goggles or face shields.

4. The principle of Prince Rupert’s drops somehow appears in the preparation of tempered glass i.e., thermal or chemical controlled hardening of glass.

Additionally, they have potential applications in specialized fields like pressure sensors and optics, where their ability to withstand high impacts can be beneficial.


Despite their remarkable strength, Prince Rupert’s drops have limitations. The tails are extremely fragile and can easily break with minimal force. Moreover, if the drop’s head is damaged, it can cause the entire drop to disintegrate. As a result, they must be handled with great care to avoid accidental breakage.

Concepts Berg

Why is Prince Rupert’s drop unbreakable?

Prince Rupert’s drop is unbreakable due to its unique internal structure. The rapid cooling during its formation creates compressive stress on the outer surface and tension in the interior, making the head highly resistant to external forces.

Why Prince Rupert’s drop is so strong – stronger than a bullet?

Prince Rupert’s drop is exceptionally strong due to the distribution of forces caused by its unique internal structure. The rapid cooling process results in compressive stress on the outer surface and tension in the interior, allowing the drop’s head to withstand the impact of a bullet.

What is so special about Prince Rupert’s drop?

The special properties include; a strong head & fragile tail.

Is a Prince Rupert’s drop stronger than steel?

Yes, in certain aspects, a Prince Rupert’s drop can be stronger than steel. Its head can withstand considerable external forces, but it is important to note that steel has broader applications and overall higher strength in various contexts.

Is Rupert’s drop stronger than the diamond?

No, Prince Rupert’s drop is not stronger than a diamond. While the drop’s head can resist some external forces, diamond is renowned for its exceptional hardness and is considered one of the hardest materials known.

Can a bullet break Prince Rupert’s drop?

No, usually a bullet cannot break Prince Rupert’s drop. The drop’s head is highly resistant to external forces, including bullet impacts, due to its unique internal structure formed during rapid cooling.

What is the hardest glass to break?

The hardest glass to break is Borosilicate glass. It is highly resistant to thermal shock and has superior strength compared to regular soda-lime glass, making it more difficult to break under various conditions.

Is Prince Rupert’s drop invincible?

While its head is highly resistant to external forces, it can still be shattered if the tail is damaged, causing the internal tension to be released and leading to its complete fragmentation, therefore, it is not invincible.

Are Prince Rupert’s drops dangerous?

Prince Rupert’s drops can be dangerous if mishandled or broken. The fragments of the tail can shatter with force, potentially causing injuries.

What would happen if you remove the tail from Prince Rupert’s drop?

Removing the tail compromises its stability and leads to the fragmentation of the entire drop.