Exam (elaborations)

COIN HOARD FROM VARUDI – VANAKÜLA. QUESTIONS AND ANSWERS IN CONSERVATION

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COIN HOARD FROM VARUDI

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COIN HOARD FROM VARUDI

A. VILJUS and M. VILJUS 602 INT J CONSERV SCI 8, 3, 2017: 599-606 In order to remove corrosion products several chemical solutions were tested. Formic acid, phosphoric acid, alkaline Rochelle salt and ammonia solutions were experimented, starting with 5% concentration and three hours, up to 15%...

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INTERNATIONAL JOURNAL
OF

CONSERVATION SCIENCE
ISSN: 2067-533X Volume 8, Issue 4, October-December 2017: 599-606 www.ijcs.uaic.ro

COIN HOARD FROM VARUDI – VANAKÜLA.
QUESTIONS AND ANSWERS IN CONSERVATION

Aive VILJUS1*, Mart VILJUS2
¹ Tallinn University, Archaeological Research Collection, Rüütli 10, 10130 Tallinn, Estonia.
² Tallinn University of Technology, Centre for Materials Research, Ehitajate tee 5, 19086 Tallinn, Estonia.

Abstract

The article discusses the conservation issues of Roman coins on the example of a specific find,
gives an overview of the conservation process and material studies. It analyses corrosion
products and the historic patina survived on the coin surface. The author endeavors to
establish connections between the composition of the coin metal and corrosion.

Keywords: Roman coins; Conservation, Composition of metal; Corrosion; Patina.

Introduction

In April 2015 hobby archaeologists and archaeologist Ain Mäesalu, who were looking
for the site of a historic battle in the landscape, came across a hoard near Uhtna, Lääne-Viru
County, which consisted of coins and various ornaments. Initial examination verified that the
coins were apparently sestertii from the era of the Roman Empire. The find, consisting of 51
coins, immediately doubled the number of Roman coins registered in Estonian museums, since
so far Roman coins had been discovered in Estonia only on rare occasions.
The treasure was discovered from an old hayfield on a river floodplain by a bridge. Upon
discovery the coins and ornaments were not in their original hiding place anymore: XXth
century drainage and ploughing had spread them over a few square meters wide area. At the
time of hiding the area was rather moist, therefore it cannot be associated with a former
settlement [1]. Money was not known in this region at the time, therefore coins must have been
used as raw material for e.g. jewelry, weights or luxury items.

Materials and methods

Conservation
Decisions taken by the conservator determine the appearance of the monument or the
artefact. Hence the responsibility of the conservator is enormous: he/she must elaborate the
critical decision on the object itself. Historians may change their mind and re-evaluate their
opinions at any time, the decisions of the conservator will permanently survive on the object.
All objects made by man, i.e. artefacts are historical documents that carry data about the
materials used, working methods and techniques applied. Time passes and adds its marks,

*
Corresponding author:

, A. VILJUS and M. VILJUS

which are regarded as material expressions of historicity, summarized in the term patina.
Therefore patina is considered as an integral part of the original substance, brought to us
through history. Any attempts to remove it will harm the original substance of the object and
lead to historical contradictions, since patina-free old objects appear as fresh and made of new
material [2].
Switching from conservation philosophy to practical conservation activity: the patina on
archaeological bronze items may be categorized into three layers [3-10]:
- Primary (or precious) patina that has formed in the process of making and using the
object, mainly in contact with Oxygen and Sulphur.
- Secondary patina, which starts to develop when the object gets into the soil and which
may be also called corrosion layer. The main factors here are moisture, oxygen, aggressive
(acid or alkaline) environment and chlorides.
- Depending on the properties of the soil and the length of time in ground, some objects
may have tertiary patina, which develops as a result of mineralization and fossilization of
secondary patina and mixing with the earth, and which sometimes is called concretions.
The process of conservation should distinguish between those layers, focusing on
preserving primary patina as much as possible, and removing later corrosion products.
Various chemical and mechanical treatments may cause physical loss in the object’s
structure or material, which in turn will bring about losses in historical or esthetical values [11].
But it may also be the other way round – bringing forward or making the original image of the
object visible may provide significant new information and so supplement the so-called historic
document, which coins first and foremost are.
The main objective of the current conservation work was to find a method that would be
least harmful to the coins in order to preserve as much information as possible for numismatists
and historians. Therefore it was decided that removing the active corrosion layer could only be
done to the extent that it would not damage the coin surface or historic patina. Practical
conservation was complicated, because so far only few Roman coins have been found in
Estonia and there was lack of earlier experience in this field. The best method had to be found
in the actual conservation process, considering the preservation state and properties of the
material, which became evident in the work process.
State of the coins
The coins were brought to the conservation laboratory at the next day after the
excavation. They were packed in reclosable plastic bags together with moist soil, to prevent the
coins from drying. The coins seemed to be in good condition, the level of surface damage was
more difficult to assess, because the coins were covered with soil residue and corrosion
products (Fig. 1). The method of radiography was applied to determine the level of damage on
the surface, unfortunately it did not give the expected result. The X-ray photos failed to bring
out details of the stamp, but they affirmed that generally the coin metal had well preserved.
Only a few coins demonstrated cracks on the edges and slots on the metal surface.
Initial observation suggested two groups of coins:
1) Coins with surfaces covered with historical patina and a fairly thin layer of corrosion,
surface relief identifiable. Such coins were in minority (Fig. 2)
2) Coins with surfaces densely covered with a thick layer of corrosion products, surface
relief un-identifiable. Surfaces of the coins were generally covered with a thick black corrosion
layer with crystalline products, the like of which the author had never before encountered on
items of copper alloys, and which alternated with green corrosion (Fig. 3). Such coins formed
the majority.

600 INT J CONSERV SCI 8, 3, 2017: 599-606

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