The six-board chest is another, albeit much lesser-known, example of convergent design. While most boxes and chests have six sides, “six-board chests” are identified as such not by the number of sides they have, but by the contradictory grain orientations of the front / back and side boards. The front, back, bottom, and lid all have horizontal grain orientation, while the sides run vertically, making them – as modern-day woodworker Christopher Schwarz puts it – the “platypus of the woodworking world.” Why is that so bizarre? Because they are made from wood, and wood as a building medium is subject to inevitable expansion and contraction alongside changes in humidity and temperature. Misaligned grain can cause cupping, twisting, and other problems. Because the components of these chests will shrink and expand constantly, and in different directions at the same time, this style of construction shouldn’t actually work. Despite all this, many six-board chests have survived hundreds of years, and the construction style itself has persisted in popularity and utility for at least a thousand years. Examples of these chests have been found throughout multiple woodworking civilizations, and though many have tried to improve upon the design, the soundest version seems to also be the oldest. This Old Norse forebear of the six-board chest goes by few different names, predominately viking chest, sea chest, and 5˚ chest.
The oldest Norse sea chests discovered to date range from 900 A.D. to 1100 A.D., putting them soundly within the Viking Age, before friendly contact with Europe would begin to noticeably influence Old Norse technology and craft. These sea chests exhibited a few unique features not observed in the six-board chests being crafted in Europe at the same time. The most noticeable characteristic is the four inward-sloping sides, the reason for the 5˚ chest nickname. Of note, none of these chests had consistent 5˚ sloping corners, tending to range somewhere between 3˚ and 10˚ even within a single chest.
–Kate Fox, excerpt from “Convergent Design: The Six-board Viking Sea Chest,” in Issue Five