Metals Conservation: 16th century padlock

Posted on 19th July 2024

By Conservation studies student, Katherine Hernon-Johnson, who specialises in Metalwork

I come from a fine art background and graduated in 2020. I specialised in sculpture exploring drawing within the theme of nature; cycles and folklore. It is subsequently where I first learnt to weld before spending time in a garage during lockdown practising my welding and helping with the cars when needed.

The qualities of a material and how it can be used and manipulated I have used intuitively to create my work. This has crossed over into conservation regarding learning the structure of metals and how and why it corrodes. Understanding a material aids in its treatment as well as being able to problem solve how to repair a metal object based on the qualities of the material.

The project began with an etched image of a square padlock with removable hasp dating from the 16th/17th century, and the goal was to recreate a working version of the padlock as closely to the image as possible. The proportions of the padlock were based on a padlock with the same hasp/ shackle found on an auction website.

The main issues pertained to the parts that could not be seen such as the shape of the bolt and where the spring would be located and how it interacted with the bolt. The final result had a separate spring that pushes against the bolt to keep it closed.

I had made one padlock previously and designed every aspect of it. Trying to fill in gaps of a partially completed puzzle requires a different problem-solving approach as there is only so much that can be changed to make the mechanism work and additions must fit with what has already been provided.

Following the completion of the padlock it was artificially corroded using an atmosphere of Hydrochloric acid as well as dripping the solution directly on to the surface in areas.

Where the Hydrochloric acid had been dropped directly on to the surface of the front plate, an almost glassy layer had been created and the combination of brass and steel created areas of galvanic corrosion. The next step of the project was to restore the padlock to its original condition or as close as possible. As the spring was still intact (indicated by the padlock opening and closing) I made the decision to not open the lock at this stage and risk harming the mechanism.

The cleaning of the padlock was achieved using a combination of solvent (Industrial methylated spirit, white spirit) and mechanical cleaning (scalpel, wire brush). Chelators were also trialled and left on for longer than necessary to see what could be done to rectify what had been done in a similar situation.

The inside of the padlock was investigated with non -invasive procedures such as an endoscope to take pictures without needing to cut open the padlock. The endoscope requires being plugged into a computer, selecting the camera input and afterwards Images show heavily corroded interior. Although the padlock worked, I decided to see if I could tackle the corrosion inside. However, that appeared to be a mistake as I inadvertently triggered active corrosion to start again, sometimes it is better to leave things as is to avoid creating a new problem. This was addressed using WD40 to arrest the corrosion and the oil was removed from the outside using white spirit. The reactivated corrosion caused the post that the key slid on to, to become loose and eventually detached. The post is now soldered into the key in order to keep the padlock as a working example as adhesives are not strong enough to keep the post in place indefinitely.

This project combined hand skills with problem solving and a hands-on example of how ferrous metal as well as the copper alloy ‘brass’ reacts to environments and treatments. It combined research and active thought regarding conservation ethics guidelines regarding what is appropriate when choosing a particular treatment for the object. Approaching the restoration half as a conservator rather than a maker allowed room for experimentation and the utilisation of invasive and non-invasive approaches to treating the padlock and getting it working again when things go wrong. If I had approached it as a maker, I’d have sandblasted and re-patinated the surface to return it to its original state, which would have limited the learning potential.