Conservation of a Copper Alloy Breech Chamber from the Rooswijk

What is a breech chamber and how does it work?

The advantage of a breech loading cannon over a standard muzzle loading cannon, was that the chamber could be prepared in advance and loaded swiftly to fire shot. A breech chamber would be pre-loaded with gunpowder and projectiles and a wooden tampion would be used to seal the chamber during storage. When required the tampion would be removed and the chamber would be loaded into the cannon. The chamber key would interlock with a specific gun. The touchhole would face upright with a wick most likely made of cordage which would be lit to ignite the gunpowder within the chamber, firing the shot. The Rooswijk would have had a number of cannons and specialised crew working under a Master Gunner to maintain and fire the weaponry. Of the Rooswijk crew identified none have been noted to have held the role of bosschieter (gunner) on the Rooswijk. Laurens Hansen (Second mate) and Cornelis Mazier (boatswain) were found to have served as a bosschieter on previous vessels so it is possible they may have assumed this role if the need arose (De Windt. M, Lucassen. J, Van Rossum. M 2017, p. 201).

What do the markings mean?

Continuing from the tradition of marking guns with the emblems and monograms of nobility, major trading companies would mark their cannons with their initials or logo. Markings could also denote information about the cannon. From the breech chamber markings we know the following:

A: Amsterdam

VOC:  Verenigde Oost-Indische Compagnie (translation: United East India Company)

30: 30 Amsterdam pounds

I N D.: Ioan Nicolaas Derck, the initials of the gunfounder

An Amsterdam pound was 494 grams whereas a British pound was 454 grams. This meant that a Dutch gun with a calibre of 12lbs (5,443 kg) would have a larger bore diameter than a British gun of the same calibre. The 30 marking denotes the weight of the chamber as gunfounders would be paid by the weight of the gun (Brinck. N 2020, p. 70). 30 Amsterdam pounds is roughly 32 British pounds. The weight of the conserved breech chamber was 31.83lbs (14,437 kg).

How was it made?

The casting of bronze guns was costly and the Rooswijk was likely fitted with iron cannon (Brinck. N 2020, p. 40). However, the retrieval of the breech chambers would suggest the presence of Bronze ordinance. In the 18^th century there were a number of foundries casting bronze guns within the Netherlands. Few artefacts in the Rooswijk assemblage can be tied to an individual so it is particularly exciting the breech chamber bears the initials of the gun founder Ioan Nicolaas Derck. Derck was a gunfounder in Hoorn in the province of North Holland, a former Dutch East India Company base. He worked from 1714 until his death in 1764 after which his widow took over the foundry and produced guns for a further 10 years (Brinck. N 2020, p. 288). Further notes on manufacture can be deducted from the chamber’s appearance. There are faint cast lines on the base, on the top and running under the handle of the chamber. This would suggest the chamber was cast in a two-part mould. Understanding the manufacture makes it possible to make informed conservation decisions regarding the iron corrosion deposits left by the chaplets. The two iron chaplets acted like pins and would have held in place a central dowel used to cast the chamber bore. As these showed no active iron corrosion, they are considered stable. They represent a stage of manufacture and it was decided to leave the chaplets in situ.

Excavation and Conservation

The decision was made to sample the deposits within the bore as the chamber had the potential to contain gunpowder. The mouth of the breech chamber was covered in a thin layer of concretions. These were carefully removed with an airscribe. No tampion or wood remains were discovered during deconcreting. Behind the concretion was a thick, dark brown, granular deposit mixed with seawater. This was sampled carefully using a rubber scoop to avoid scratching the interior chamber. Several rinses from within the chamber were also retained for analysis. The touchhole was excavated using a wooden skewer but was found to contain soiling only with no cordage sample from the wick. After cleaning and desalination, the chamber was solvent dried and placed in desiccated storage.