A selection of silver coins, including some snipped fragments.
A selection of silver coins recovered from the Rooswijk. © Rijksdienst voor het Cultureel Erfgoed/Historic England
A selection of silver coins recovered from the Rooswijk. © Rijksdienst voor het Cultureel Erfgoed/Historic England

Rooswijk Shipwreck Excavation The Post Excavation Phase

Find out how a team of specialists is researching and conserving the artefacts from the shipwreck of the Rooswijk.

The Rooswijk was a Dutch East India Company vessel which sank on the treacherous Goodwin Sands, off Kent, in January 1740. The ship was outward bound for Batavia (modern-day Jakarta) with trade-goods. Now a protected wreck site the ship's remains lie at a depth of some 20 metres. They are owned by the Dutch Government and managed by Historic England on behalf of the Department of Digital, Culture Media and Sport.

The #Rooswijk1740 project is led and financed by RCE - the Cultural Heritage Agency of the Netherlands, as part of the Dutch Ministry of Education, Culture and Science. In collaboration with Historic England and the dive contractor/ post excavation manager MSDS Marine Ltd. two seasons of excavation took place in 2017 and 2018. Historic England is providing specialist and research facilities for the post-excavation phase.

On this page you can find out:

How we are conserving maritime finds

The artefacts recovered during the excavations in 2017 and 2018 have been transported to our research facilities at Fort Cumberland, Portsmouth.

The video shows time-lapse film of finds being moved from a flat-bed lorry to a storage tank in order to keep the finds stable.

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One of the first things was to assess everything. In other words, we took stock: how much have we got, what have we got, what can that tell us about the wreck, what condition are artefacts in and what do we need to do next. This is a crucial step, as it will allow us to plan and budget for the next phase of work.


We initially undertook a program of X-radiography. This allowed us to assess the internal structure and condition of artefacts in a non-destructive way. This was especially important for the many concretions that were recovered.


A concretion forms around an iron object and can encase anything in the surrounding areas, such as sediment, stones, sea shells, and other artefacts. We use these X-ray images to identify what is inside the concretion and as a guide when we come to remove the artefacts.

In some cases, removing artefacts from concretions may not be possible, or it may be too time-consuming or even damaging. Read this blog to find out what we can do in such cases.


Artefacts removed from concretions and all the other artefacts will go through a long process of desalination. For most artefacts this is done by regular washes in distilled water. Other materials, such as iron or copper alloys require chemicals to remove harmful salts.

Further Treatment

Once artefacts are desalinated, they have to be dried and can then be passed on to the relevant specialists.

Sometimes we may carry out more interventive treatments, such as re-assembling this mallet shaped glass bottle.

Next steps will involve starting work on the conservation of wooden artefacts and on the larger concreted chests and containers. One large cask has already been deconcreted. This allowed us to record its construction and examine its content: hundreds and hundreds of iron nails.

How we are analysing different materials

When the Rooswijk was lost in 1740, the pace of technological development was increasing to such an extent that the next 100 years are commonly known as the industrial revolution. There was fierce global competition amongst manufacturers and traders, and chemical analysis can tell us more about this by establishing where and how objects were made.

Glass Beads

Some of the smallest objects recovered from the Rooswijk are tiny brightly coloured glass beads that were made in volume in Europe for export because they were highly valued on other continents. A lot of the plain yellow and green Rooswijk beads are made from lead glass, and their lead content makes them visible as bright specks on X-ray images.

A scanning electron microscope reveals that the plain white beads were manufactured in a more complex process. They are not lead glass and, although only a few millimetres wide, they are made in three layers (two white and one clear).

The most elaborate multi-coloured or 'polychrome' bead was made from multiple layers of glass in strong colours, and then partially ground away at the ends to create a chevron pattern.

Other Glass Artefacts

A drinking goblet on board was made with quality colourless glass from Bohemia (now the Czech Republic) and the recoveries included glass lenses made from specialist colourless glass.

The wine and gin bottles were blown from cheaper common green glass, which were probably sourced from several countries to meet demand.

Silver Coins

The archaeologists recovered a lot of silver coins at the wreck site. Some of them are Dutch coins (Rider, Ducaton and Schelling), while others (Cob 4, Cob 5 and Pillar dollar) are coming from the Americas.

The composition of the coins was studied in order to get information about the monetary system, to get numismatic information, and to answer questions about trade routes. The data can provide valuable information about metallurgical methods, trade relations, and the origin of raw materials. Moreover, the study of the coins with the scanning electron microscope can illustrate the state of preservation of the coins and the corrosion patina developed on the surface.

Unknown Materials

Materials science is also useful in finding out the composition of unknown substances. A sample collected from a white deposit found on the cork and around the mouth of a glass bottle was analysed by Fourier transform infrared (FTIR) spectroscopy. The sample consists of a terpenic resin, probably colophony. Colophony, sometimes also called rosin, is a tree resin of the Pinus genus. According to previous studies, natural resins and waxes were commonly used in the 18th century to seal the corks of wine bottles in order to preserve the contents.

What plant and insect remains can tell us

Tiny fragments of insects, seeds and other parts of plants extracted from sediment samples recovered from the Rooswijk wreck site will contribute to our understanding about the conditions and environment on board the vessel and the cargo and provisions carried. The many artefacts on board have acted as sediment traps, and samples of this sediment have been removed as part of conservation cleaning and processed with water to recover any plants or insect remains.

Retrieving plant and insect remains

Measured quantities of sediment from each object or find spot are placed in a bucket or bowl, water is added, the sediment is gently agitated by hand, and the lighter organic content (the flot) is poured off into a finely meshed sieve (0.25 millimetres). The fine silt is washed away and the heavy residue (sand, gravel, bits of shell and occasionally fragments of broken pottery or other finds) is left behind in the bowl.

Both the flot and the residue are then sorted under the microscope and the identifiable bits of plants and occasional bits of insects are removed.

Seeds are sorted into their botanical families based on common characteristics of shape and surface structure. Identification is then confirmed by comparing the finds with modern seeds held in a reference collection, and photographic guides. Insect fragments will be sent to an archaeoentomologist for identification.

Discoveries of food plants

Grains of wheat and fragments of cereal bran suggest whole grains had been brought on board. The internal starchy structure of cereal grains had broken down and disappeared in most of the grains, but one was intact. A fragment of corncockle seed and wild oat chaff may have been contaminants within the wheat grain. Corncockle is a classic corn field weed, the seeds of which are poisonous but difficult to eradicate from grain. If too many were eaten on board, the crew could have been quite sick, so it is likely that they would have been picked out of the grain or flour by hand as much as possible.

Seeds of flax, hemp and mustard would have provided both flavour and oil. The grain and seeds were found in sediment samples from an oil lamp, a flagon and a glass wine bottle, probably washed into the object during or shortly after the wreck event. A single bean was found lodged inside a small cylindrical container within a large concretion. Some of the seeds may have been intended for the voyage, while others may have been destined for the Dutch East Indies.

Discoveries of padding and packaging materials

A ceramic flagon may have been packed in a case full of buckwheat husks, which were recovered from the sediment samples within it. Buckwheat was commonly consumed in northern mainland Europe from the medieval period onwards, and the hard, inedible seed coat provided a useful packing medium, much like today’s sawdust or polystyrene packing chips. Some cut grass or hay may also have been used as packing material, bedding or deck covering. Seeds of grassland plants included wild carrot, knapweed, sow-thistle; these are typical of dry grassland; while sedges, club-rush, rushes, and gypsywort indicate vegetation of wetter environments.

Fragments of Sphagnum moss found in the oil lamp and a wine bottle would have had a range of purposes including for wound dressing, or filtering water, and was commonly used for caulking on boats (although the caulking on the Rooswijk seems to be made of animal hair).

It is likely that the insect fragments will provide additional information about the source of plant material brought on board, as well as the conditions within the vessel.


Finally, five coconut shells were recovered from the wreck site. The shells were complete apart from the germination holes which were open. No interior flesh remained. As the Rooswijk was outward bound from the Netherlands when it sunk the presence of coconuts is somewhat unexpected. Coconut shells were popular in Northern Europe during the 15th to 18th centuries, where they were carved and mounted, sometimes in silver or gold, as drinking vessels. Possible the nutshells were being taken to trade elsewhere in Europe, or were intended for use on board. However, coconut shells are buoyant, and it is difficult to link them to the Rooswijk with certainty. Samples of the interior lining of the shells have been submitted for radiocarbon dating in an attempt to rule out the possibility that they derive from a later cargo known to have been lost from a nearby Norwegian barque returning from Jamaica in 1889.

About the authors

Name and role

Angela Middleton

Title and organisation
Senior Archaeological Conservator at Historic England
Angela holds a degree in archaeological conservation from the University of Applied Sciences, Berlin, and an MSc in Maritime Conservation Science from the University of Portsmouth. She joined Historic England as an Archaeological Conservator in 2007. Here she is responsible for advising on and undertaking research and investigative conservation on material retrieved from land and marine sites. She has a special interest in the conservation of waterlogged organic materials.

Name and role

Sarah Paynter

Title and organisation
Materials Scientist at Historic England
Sarah Paynter studied Natural Sciences and worked in industry before obtaining a DPhil in Archaeological Science. She is now a materials scientist for Historic England and Honorary Research Fellow at the University of Sheffield. She uses analytical techniques to identify and investigate a wide range of heritage materials from buildings, collections and archaeological and maritime sites in the UK, from the Bronze Age to the twentieth century.

Name and role

Francesca Gherardi

Title and organisation
Materials Scientist at Historic England
Francesca is a materials scientist with expertise in heritage science, analysis of artworks and buildings, and conservation treatment strategy development. She performs scientific analysis of both organic (resin, gums, waxes, binding media, textiles) and inorganic (building materials, glass, metal, pigments) materials, to determine their composition and state of preservation. She is a member of the International Institute for Conservation of Historic and Artistic Works (IIC).

Name and role

Ruth Pelling

Title and organisation
Senior Archaeobotanist at Historic England
Ruth is an archaeobotanist with experience of northern European, Mediterranean and North African material. Her current role at Historic England is to provide specialist advice and sector support, to develop internal and collaborative partnership research projects, and to inform national and regional research frameworks. Her research interests include late Roman and early Islamic food and agriculture in North Africa, the past use of bracken, missing plant foods of Neolithic Britain, and aspects of British archaeobotany particularly from the Early to Middle Bronze Age and the early medieval migration period.


We thank Kamil Prus for his analysis of the glass bottles from the wreck, carried out whilst on a placement with Historic England from the University of Southampton.