By Zora Sanders
When I began my studies in Metalwork Conservation at West Dean last October, the first object I was given to treat appeared to be a fairly ordinary knife. Which just goes to show that looks can be deceptive.
Only slightly larger than the average modern dining knife, with an attractive octagonal handle and a small ring attached to the end of the handle, this knife had clearly had a hard life. West Dean metals tutor Eric Nordgren, who has many years of experience working on archaeological metals, suggested that the blade looked as though it may have been buried in mud for a long period, which led us to wonder whether it could have been a mudlarking find from the River Thames? Unfortunately, the owners of the knife, The Worshipful Company of Cutlers, couldn't provide any background information about the knife. When, where and how it came into their collection was unknown, so in the absence of any additional information I continue to think of it as a gift from Old Father Thames!
The blade showed the classic red-brown powdery surface associated with iron corrosion. Most of the blade's edge had entirely rusted away and there were plenty of holes and deep corrosion pits. The handle was generally dull and discoloured, with what appeared to be two different finishes on each alternating face.
So far, nothing too unusual. However, I started to realise this may not be a typical dining knife when I saw what was concealed inside the handle. When I pulled very gently on the finial at the tip of the knife handle (I avoided pulling on the iron ring because of its obvious fragility), a rectangular brass rod emerged. It was possible to tell from the feeling of resistance and the way it retracted back into the handle that this rod was sprung with an internal spring mechanism, similar to a modern spring balance. Along the rod were markings at specific intervals: one dot, two dots, three and then four, then one dot, two three and four repeating. It certainly seemed like whoever first used the knife intended it to be used to weigh… something.
We took the knife to nearby Fishbourne Roman Palace, where we used their x-ray machine to try and see inside the handle and understand the spring mechanism. It was difficult to get a clear image, but we could see the coiled lines of the spring wrapped around the brass measuring rod, and we could also see how much of the blade was actually just corrosion with no metal surface underneath at all.
We also performed X-ray fluorescence (XRF) on various parts of the knife and received some fresh surprises. XRF is a non-invasive technique which allows the specific elements present in an object to be identified. While the readings for the blade showed it was made from an iron alloy as we expected, the readings for the handle indicated that it was made from alternating faces of lead and a copper-alloy, likely to be a brass, and the brass faces also gave smaller readings for the presence of gold. The presence of so much lead explained why we'd had such a hard time getting clear x-ray images of the handle!
A handle made from brass, lead and gold is a pretty unusual choice, and made us all wonder yet again what exactly the knife was for? There were a variety of fairly faint markings on the handle, including a band of parallel lines around the circumference and a line of regular notches along one face, similar to the lines on a ruler. There was also a stamped letter 'H', though it really looked more like a backwards 'N' to my eye. The markings weren't confined to the handle either. On the blade someone had scratched four characters so deeply that they still showed up clearly, even in the blade's badly corroded state. They looked almost like Greek alphabet letters to be, but one of my fellow students who happens to be Greek disagreed, so their meaning and significance, like so much else about the knife, remains mysterious.
In treating this object, my goal was to improve its appearance, remove unstable corrosion surfaces and allow the more unusual aspects of the object to shine through.
I began a long and delicate cleaning process by working first on the blade. I wanted to remove as much of the loose, powdery corrosion as possible and reach a more stable surface below. I was hoping to reach the stable black magnetite surface beneath the rust, but I also didn't want to go too far and lose any of the remaining metal, or cause any further harm to the object. I slowly cleaned the blade under the microscope using scalpels and a fibreglass pen. I also washed the knife gently in industrial methylated spirits (IMS) to help dislodge the powdery rust without causing more corrosion.
When cleaning the handle, I knew I also had to be extremely gentle. Lead is a very soft metal and can easily be scratched, so scalpels were out of the question. I rubbed over the surface with cotton wool and chalk mixed with a little IMS to form a gently abrasive paste. I had observed small flecks of gold on the brass faces of the handle, but as I cleaned the surface I was surprised to see that there was actually much more gold concealed beneath the discoloured surface. As I cleaned I discovered the gold was almost pristine!
At this point I consulted with the Cutler's Company to see how they would like me to proceed. I could clean back all the gold faces to be bright and shiny, but this might look pretty strange next to the corroded surfaces on the blade and remainder of the handle. However, if I didn't clean any of the surfaces, people in future might not realise how remarkable the materials and techniques that went into making this knife really are. I felt it was important to be able to see some of the gold at least to better understand the object. Happily, the Cutler's Company agreed and together we decided I would clean one gold face but leave the others with only a light surface clean. This meant that depending on which side you look at, you can now see roughly how the handle appeared when I first received it, or how it might have looked when it was closer to being new.
After cleaning, the next task was to try and slow the continuing corrosion processes so that the knife will last as long as possible into the future. On the blade I used a tannic acid treatment. This substance converts the less stable iron compounds into more stable ferric tannate. It does also change the colour of the metal to a darker blue-black, and it makes the surface a little shinier than untreated iron would be, but it's a simple protective measure suitable for an object returning to unknown environmental conditions. Finally, I applied a coating of microcrystalline wax to the entire object and gently buffed it smooth with a cotton cloth. Again, this is a lightly protective measure that will help the metal resist unfavourable humidity and temperature conditions.
The exact use and date of the knife is still unknown. I have been lucky enough to speak about this object to many people with experience of historic objects, and although no-one has known for certain yet, there have been several fascinating theories! Some have suggested a 17th century date for it. The shape of the blade and the octagonal handle could support this, but it remains speculation for the moment.
As for the purpose, some have suggested it might be a tool for weighing mail, with the knife possibly serving as a letter opener. But the spring is very stiff, which suggests to me that it was intended to weigh something quite heavy, and indeed the markings on the brass rod measure in increments of 380 grams so it is much too stiff to weigh individual letters. Yet the knife's blade is quite modest in size, so it seems unlikely someone working with heavier materials, such a butcher or fishmonger, would have had much use for it! Also, the presence of the gold seems to suggest it had a decorative or ceremonial purpose as well as a practical one. I have jokingly suggested it might be a special 'ceremonial' cheesemonger's knife, though even for cutting cheese the blade is likely too small!
Hopefully someone out there will have an answer, but until then it has been a real pleasure to work on such an unusual, endlessly surprising object.