Diamonds - The Carrie Furnace
The diamond shapes seen on these stove pipes at the Carrie Furnace were time consuming to make and purely decorative. The audio clip describes the workers pride in their craft.
Notice the diamond shapes welded around the circumference of these stove pipes. Despite the amount of work required to cut or burn them out of sheet metal and weld them onto the stoves, they were purely decorative and the stoves would have functioned perfectly well without them. There were several thousand of them throughout the facility and they were made and welded into place as part of the pride that the craftsmen had in their work.
The decorative diamond shapes and the pride they represented to the welders is discussed in this image's audio segment.