Thirty swivel guns, or “bases”, were listed as being on board the Mary Rose when she sank, only 16 barrels were recovered.
These were breech-loaded weapons with a separate chamber, which could be removed, primed and then replaced. This was an anti-personnel weapon, positioned on a swivel that allowed it to be pointed in any direction. This mount would be fixed onto the side of the ship, and several of these mounting holes can still be seen on the gunwhales of the Mary Rose.
The gun in the foreground of the picture above had just been removed from a concretion, created by a reaction between the oxidising iron and the calcium bicarbonate dissolved in the water, which forms a hard insoluble layer around the gun. Prior to this it had been pre-washed in an ammonia solution. Afterwards, it was placed in a hydrogen reduction furnace for 100 hrs at 850°C. Then it was given further cleaning, then impregnated with epoxide resin. This process stabilises the iron, reducing the amount of corrosion.
We should point out that this is a simplified explanation – much more detail can be found in “For Future Generations”, one of the Mary Rose Trust’s official publications.