“Floats like wood” is one of those phrases that is true often enough to feel like a law of nature. It is not.
Density is the whole story
Whether something floats depends on whether it is less dense than water. Most wood is, comfortably – a great deal of a tree’s volume is air held in empty cell cavities. Balsa is the extreme case, so light it is used where weight is the enemy.
But a handful of species pack their cell walls so densely, and fill so much of the internal space with resins and extractives, that they exceed the density of water. Lignum vitae and several ironwoods sink in fresh water when dry. They are not water-logged; they are simply heavier than water, volume for volume.
The wood that was used as a bearing
Lignum vitae is the standout. It is extraordinarily dense, and it is naturally self-lubricating: its resin content means it slides against metal without added oil. For a long stretch of maritime history it was the material of choice for ship propeller shaft bearings, running underwater, where an oiled metal bearing would have been a maintenance problem. A tree, doing the job of an engineered component.
Why this matters in a workshop
Density predicts a lot about how a wood behaves under tools. Dense species dull blades quickly, resist screws unless you drill pilot holes, and can burn under a router if you push too fast. They also take an extraordinary polish – the surface can come off the tool almost glassy, because there is so little void space to interrupt it.
Very light species are the opposite: fast to work, easy to dent, and prone to tearing out unless the tools are sharp.
A note on responsibility
Many of the densest and most striking tropical hardwoods are under real pressure from overharvesting, and several are restricted in international trade. Reputable suppliers can document where their material came from. For most projects, a well-chosen domestic hardwood does everything you actually need, and there is a good argument for saving the rare stuff for the small pieces where it genuinely shows.
