- The Collaborative Numismatics Project
  Welcome Guest. Please login or register. The column on the left includes the "Best of NumisWiki" menu. If you are new to collecting, start with Ancient Coin Collecting 101. All blue text is linked. Keep clicking to endlessly explore. Welcome Guest. Please login or register. The column on the left includes the "Best of NumisWiki" menu. All blue text is linked. Keep clicking to endlessly explore. If you have written a numismatic article, please add it to NumisWiki.

Resources Home
Home
New Articles
Most Popular
Recent Changes
Current Projects
Admin Discussions
Guidelines
How to

Index Of All Titles


BEST OF

AEQVITI
Aes Grave
Aes Rude
The Age of Gallienus
Alexander Tetradrachms
Ancient Coin Collecting 101
Ancient Coin Prices 101
Ancient Coin Dates
Ancient Coin Lesson Plans
Ancient Coins & Modern Fakes
Ancient Counterfeits
Ancient Glass
Ancient Oil Lamps
Ancient Weapons
Ancient Wages and Prices
Ancient Weights and Scales
Anonymous Folles
Anonymous Follis
Anonymous Class A Folles
Antioch Officinae
Aphlaston
Armenian Numismatics Page
Brockage
Byzantine
Byzantine Denominations
A Cabinet of Greek Coins
Caesarean and Actian Eras
Campgates of Constantine
Carausius
A Case of Counterfeits
Byzantine Christian Themes
Clashed Dies
Codewords
Coins of Pontius Pilate
Conditions of Manufacture
Corinth Coins and Cults
Countermarked in Late Antiquity
Danubian Celts
Damnatio Coinage
Damnatio Memoriae
Denomination
Denarii of Otho
Diameter 101
Die Alignment 101
Dictionary of Roman Coins
Doug Smith's Ancient Coins
Draco
Edict on Prices
ERIC
ERIC - Rarity Tables
Etruscan Alphabet
The Evolving Ancient Coin Market
EQVITI
Facing Portrait of Augustus
Fel Temp Reparatio
Fertility Pregnancy and Childbirth
Fibula
Flavian
Fourree
Friend or Foe
The Gallic Empire
Gallienus Zoo
Greek Alphabet
Greek Coins
Greek Dates
Greek Coin Denominations
Greek Mythology Link
Greek Numismatic Dictionary
Hellenistic Names & their Meanings
Hasmoneans
Hasmonean Dynasty
Helvetica's ID Help Page
The Hexastyle Temple of Caligula
Historia Numorum
Horse Harnesses
Identifying Ancient Metal Arrowheads
Illustrated Ancient Coin Glossary
Important Collection Auctions
Islamic Rulers and Dynasties
Julian II: The Beard and the Bull
Koson
Kushan Coins
People in the Bible Who Issued Coins
Imperial Mints of Philip the Arab
Later Roman Coinage
Latin Plurals
Latin Pronunciation
Library of Ancient Coinage
Life in Ancient Rome
List of Kings of Judea
Malloy Weapons
Maps of the Ancient World
Military Belts
Mint Marks
Monogram
Museum Collections Available Online
Nabataean Alphabet
Nabataean Numerals
The [Not] Cuirassed Elephant
Not in RIC
Numismatic Bulgarian
Numismatic Excellence Award
Numismatic French
Numismatic German
Numismatic Italian
Numismatic Spanish
Parthian Coins
Patina 101
Paleo-Hebrew Alphabet
Phoenician Alphabet
Pi-Style Athens Tetradrachms
Pricing and Grading Roman Coins
Reading Judean Coins
Representations of Alexander the Great
Roman Coin Attribution 101
Roman Militaria
Roman Mints
Roman Names
romancoin.info
Rome and China
Satyrs and Nymphs
Scarabs
Serdi Celts
Serrated
Siglos
The Sign that Changed the World
Silver Content of Parthian Drachms
Star of Bethlehem Coins
Statuary Coins
Sylloge Nummorum Graecorum
Syracusian Folles
Taras Drachms with Owl Left
The Temple Tax
The Temple Tax Hoard
Test Cut
Travels of Paul
Tribute Penny
Tribute Penny Debate Continued (2015)
Tribute Penny Debate Revisited (2006)
Tyrian Shekels
Uncleaned Ancient Coins 101
Vabalathus
Venus Cloacina
What I Like About Ancient Coins
Who was Trajan Decius
Widow's Mite
XXI

   View Menu
 

Crystallized

Ancient silver coins are sometimes extremely brittle. This brittleness is found in coins which are corroded as well as in coins which show no sign of external corrosion. Unfortunately, almost any ancient silver coin might suffer from undetectable crystallization. Fortunately, the vast majority of ancient silver coins are not crystallized or especially fragile. When a crystallized coin is dropped on a hard surface or handled roughly, it may break. While the exterior of the coin appears to be normal silver, the interior is white and does not appear metallic.

Although crystallization is the popular term used to describe this fragile condition, the term is a misnomer.  Granularization or embrittlement are perhaps better terms (but not customary).  Embrittlement of silver has been studied for a long time. It is the cause of some concern in museums holding archaeological silver and in archaeology itself. Embrittlement seems to be linked to inter-crystalline corrosion (see Ravitch, Lehmann, Organ, and Werner). Inter-crystalline corrosion can be exacerbated by the alloying elements present in the silver. Copper and lead are commonly encountered in brittle silver (Lehmann, Bhowmik, Toda, Thompson) but bismuth has also been detected (Rematullah). Discontinuous preservation of copper at the edges of the silver grains can also lead to embrittlement. Lead can make silver brittle even without corrosion (Toda).

References:

Thompson, F. & A. Chatterjee. "The age-embrittlement of silver coins" in Studies in Conservation Vol. 1 No. 3, 1954, pp. 115-126.

Ancient silver objects are often found to be in extremely brittle condition. This brittleness can be observed in objects which are corroded as well as on those which show little or no sign of external corrosion. The brittleness of apparently uncorroded silver objects represents an interesting metallographic problem since the silver must have been ductile at the time the object was manufactured. The embrittlement implies a drastic change in the metallographic structure. The research laboratories of the Musie d'art et d'histoire in Geneva and the Metropolitan Museum of Art in New York City are collaborating on a project to study changes in the microstructure of silver-rich silver-copper alloys from long exposure to ambient temperatures. After preliminary work on a scanning electron microscope, microhardness tests, and examination of metallurgical cross sections of silver samples dating from 500 B.C. to A.D. 1000, research is now centered on copper precipitation from the silver-copper alloy. The binary-phase diagram for the silver-copper system shows that up to 8% of the copper will remain in solution at the eutectic temperature but that the silver can hold only one-tenth percent copper at room temperature. The precipitation of copper from the super-saturated solid solution occurs rapidly at temperatures between 150 and 450C, but very slowly below 100C. C. S. Smith suggested that a small but visible amount of copper could precipitate even at room temperature over many centuries. This type of precipitation is called "discontinuous" or "cellular." Precipitaion behavior of modern silver-copper alloys is discussed and compared with the observed microstructures of ancient silver samples. The possibilities and limitations of a new method of authentication by measuring the interlamellar distance between the copper-rich precipitates is treated.

Kallfass, M., P. Juergen & J. Hermann. "Investigations on the embrittlement of an antique Roman silver bowl" in Prakt. Metallogr (0032-678X) Vol. 22 No. 7, 1985, pp. 317-323.