11 May 2018

How to treat a rare 17th Century Dutch chart

by By Chloe Mills, Paper Conservation Intern

This chart and other fascinating objects are on display in the Pacific Encounters gallery.

I knew I was going to be working on this piece within the first few days of my internship. This was a very daunting task given both the age and rarity of the chart. It was produced by Dutch ‘Golden Age’ Cartographer Claes Janszoon Visscher in 1650 and is one of only two known copies. It measures 1120mm x 815mm and depicts a highly detailed world map as seen by the Dutch in the 17th Century.

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Detail of two fisherman. A trademark of Visscher’s and what’s believed to be the personifications of the cartographer as a boy and an old man.

As was common for the time, the chart is themed to reflect the power and sovereignty of the country. It also depicts the first Dutch round the world voyage taken by Olivier van Noort (1598-1601). Six scenes illustrating triumphant Dutch voyages are also illustrated within the elaborately detailed borders.

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The overall condition of the chart was poor. It was strongly discoloured all over with disfiguring orange stain spots. It had an overall light covering of surface dirt and was suffering distortion and curling at the edges. The paper felt very brittle and had tears and losses throughout, especially at the corners and edges. It had also clearly been a tasty meal for insects, which had resulted in many holes. Some of these insect holes had been filled in with card and the missing image had been re-drawn using graphite pencil.

The chart was originally printed in four parts from four different sized copper plates. However, when the chart came into the collection in the 1930s it was in eight pieces which had been joined together with a thick patchwork backing formed of several layers of paper. I immediately noticed that the backing appeared to be putting strain on the chart and was reacting with the surrounding environment causing distortion and curling. The adhesive used was also causing discolouration, staining and acidity making the paper brittle.  

The paper felt very brittle and had tears and losses throughout, especially at the corners and edges. It had also clearly been a tasty meal for insects

Here I had a tricky conservation treatment decision to make; to remove the backing or to maintain it. Removing the backing would significantly improve both the chart’s stability and its aesthetic appearance. However, while the backing layers were unlikely to be original, they were still historical to the chart. I decided to investigate potential treatments for improving the chart whilst keeping the backing layers but concluded that deterioration would continue to occur with the backing left in place.

After sharing my results and discussing my options with the conservation team and the curator of maps and charts, I decided that it would be best to remove the backing layers, but to do so in a way that allowed for future research if necessary. My approach would involve solubilising the adhesive between the layers allowing me to gently peel them away. The risk with this method was that adhesive would move into the chart and cause more staining. To prevent this, moisture needed to be introduced gently and carefully, so good judgement and timing was key.


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Removing the backing

Before removing the backing layers, each section was surface cleaned and fragile areas protected with facing patches of tissue and methyl cellulose. Each section was humidified and then placed into ‘a sandwich’ of Goretex (a semi-permeable membrane that allows moisture vapour to move in one direction only), damp blotters, polythene sheets and hard acrylic sheets. This sandwich method allowed me to keep the chart section humidified whilst I worked to remove the adhesive and backing.


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Screen washing


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Before/after washing

The next step was to wash the chart sections and draw out discolouration and staining while reducing acidity. This was done using two methods, screen washing and suction table washing. Both methods were carried out with a strict methodology to ensure a consistent finish. Once the washing was complete it was left to dry and then repairs to the paper were carried out. For this I used layers of toned Japanese paper and wheat starch paste.

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Backing layer


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Backing layers humidified and flattened for storage

Mounting for display

The final step in the treatment was to mount the chart for display. This was particularly tricky given the haphazard way in which the chart had been cut into eight sections. Navigational lines, edges of countries and many other details on the chart could not be aligned. The mounting of the chart required a lot of minute adjustments and I used Japanese tissue to soften the appearance of gaps. This required a lot of patience but the final result was definitely worth the perseverance.

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The chart is now complete and ready for display. The conservation treatment improved both the visual appearance and the strength of the paper and the mounting enhanced the readability of the chart. I urge you to go and see this brilliant chart in the new Sackler Gallery: Pacific Encounters. I’m sure you will get as much enjoyment from it as I have.