Prince Rupert's Drop
The Prince Rupert's Drop is an experiment that illustrates stress distribution. To perform this experiment, glass is gathered from the furnace and dropped into a bucket of cold water. The outside of the drop cools down rapidly and forms a high amount of compression on the outer surface. While the drop is still in the water, it starts to cool the inside layers. This causes a very high tension inside the drop. At this point, no matter how hard you strike the bulb, it will not break. To break it, you have to crack the interior tension zone. This zone is most easily cracked in the tail portion of the drop. When you break the tail part of the drop, you release a chain reaction. This cascade of energy travels from the tail to the bulb; decompressing the high tension and the outer surface causing the drop to explode!
A similar lesson is illustrated with crackling the glass. The glass is rapidly cooled by dipping the molten glass into a bucket of water. Where the water cools the glass surface and the glass contracts. The still hot inside layer creates tension and cracks the surface as a result.
When atoms are heated to high temperatures, some electrons may absorb enough energy to allow them to “jump” to a higher electron level. When cooled, they release extra energy in the form of light. We often see this as color. Fireworks are a good example of electrons releasing energy.
The appearance of glass may be changed by robbing the color of oxygen when the glass is being heated. With oxygen removed, the metals in the color bond to the surface of the glass and appear discolored, often metallic.