A Deck Prism was fitted into a ship’s deck to illuminate the areas where sunlight could not penetrate. For centuries, sailing vessels used the reflection and refraction from deck prisms to provide light on board wooden ships. Though candles and kerosene lamps were also used, these posed a hazard.
Meanwhile, the glass prism dispersed the natural sunlight into the space below from a small deck opening without compromising the vessel’s seaworthiness.
Usually, it hung below the overhead and dispersed light in a sideward fashion. The top was flat and had a flush with the deck, ultimately becoming a part of it. The lens shapes were naturally derived from handmaking the glass on an iron.
To get the areas lit brightly, the glass was made colourless with manganese oxide while the purple hue of some specimens found was caused by years of exposure to UV rays.
Onboard colliers or coal ships, these prisms were used to keep an eye on the cargo holds. A fire was lit which was then reflected by the prism and could be seen on the ship’s deck even during the day.
