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Archaeology conservation: find out how its done!

Helen Cunningham-Johns is a student at Cardiff University undertaking conservation work on the finds from our 2019 dig. As part of her project she is analysing the iron artefacts discovered on site. Below she guides us through the process step by step:

1. Shooting the x-rays

The Iron artefacts arrived separated into their boxes based on where they were found. The objects were placed over a folder containing the film and a piece of paper that would later be used to house the x-rays. The artefacts were then roughly drawn around in pencil so I could see a general shape and match this to the objects once complete.

Some of the boxes contained items of different weight, density and size so multiple exposures with a different power and exposure time would have to be done; such was the case with the objects shown in the photographs below. You can do this easily with the use of leaded sheets to protect the side of the film you don’t want exposed to the x-rays and then swapping it over to the other side for the next x-ray.

We have to write down every x-ray we do to keep an accurate record. These records include the material the items are made of, the exposure time and the power. They also act as a handy reference for the power and exposure time that have been used on similar items in the past. Because of the health and safety risk, you can only start the x-ray machine from outside the room and have to wait until its finished before you can enter again.

2. Developing the x-rays

Once the x-rays are shot we can take the film down to the dark room to be developed. We have to keep the room dark to prevent the film being exposed to light before it’s developed. There are 3 successive baths they have to go into with a specific time needed in each bath. After they’ve gone through the first developing bath the lights can be switched on again (unless you have another x-ray to start developing!). Once fully developed they need to be rinsed for around 30 minutes to remove any left over chemicals and can then be hung to dry.

3. The final x-rays and what they show us

Here are some of the finished strata artefact’s x-rays! X-rays are useful as they can show us how deep the corrosion or dirt layer is around an artefact. The cloudier the image, the less dense the material. Corrosion is much less dense than the original metal so appear cloudy compared to the metal objects, which are white. They can also show if any original material is left or if it has completely corroded leaving a shell behind of just corrosion products. We can also see features that aren’t necessarily visible in person, such as the holes and pins in the bottom right artefact in x-ray K135.

4. Conservation of the iron finds

Now that the x-rays are done, we can make some decisions about whether there are any objects that look particularly interesting and can undergo conservation treatment to remove the dirt and corrosion. Until we decide, all the boxes the objects are stored in have had bags of silica gel placed in them to keep the humidity down. This will stop moisture from reaching the objects and causing even more corrosion.

Once we’ve decided which ones we want to conserve there are a number of different conservation treatments we can look into. This could include using an air abrasive machine to ‘blast’ the corrosion layers of the surface away or using a scalpel to scrape it off. There are lots of pros and cons that are associated with each treatment process and the decision can only be made once we’ve decided what the aims of the treatment are and whether it’s appropriate to use these processes on these objects in particular.

Helen will be telling us more about her findings and other processes involved in the conservation of these items - check back here for more updates!

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