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SilverHistory and Conservation
Robert van LanghHead Metals ConservationRijksmuseum Amsterdam
Senior Lecturer Archaeologic & Historic MetalsNetherlands Institute for Cultural Heritage
Worcester, June 2 (8.30 – 10.30 hrs), 2005
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Bowl and ewer, Joh. Lutma, 1646
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Content
• Vulcan’s workshop• Authentication and microscopic research • Current and ongoing research• Do we know everything of the
conservation of silver?• My questions for you
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Vulcan’s workshop
The rolling mill on depictions of Vulcan’sworkshop in the 17th century
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Vulcans’ forge 1608,Jan Breughel (the velvet,1568-1625), Ambrosiana, Milaan
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Detail
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Vulcans’ forgeJan Breughel (the velvet, 1568-1625)
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Detail
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Vulcans’ forgeJan Breughel (the velvet, 1568-1625)
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Detail
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Use of the rolling mill in the 16th century
French king (31/3/1547-10/7/1559)
Henry II buys in Augsburg 1551
• Rollingmills• Drawbenches• Punch• Mintagepunch• Fasteners for
stampholders
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Dutch use of the rolling mill in the 17th century
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Using horsepower
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Perspective drawing
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Built up of the rolling mill
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The current rolling mill
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Example of possible use
Rijksmuseum,BK-17041-A, Globe, 1709Augsburg
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Thickness = 0,8 mm
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Microscopic research
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Making the microstructure visible
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Grain boundaries
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∆T
∆T
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Microstructure of silver
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Microstructure of milled silver
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Copper coin found on the wreck of the Zuytdorp, 1712
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Legacy F.G.S. Baron van Brakell tot den Brakell, 1878
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Historic comparison
Unknown, Rijksmuseum Amsterdam
Hans Jakob Mair, 1674, KMKG Brussel
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Dwarsdoorsnede van een sampleCross section Ag (ca. 300 µm in to
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Exfoliation of Silversulphide
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A new method for treatment
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Exfoliation
Formation of silversulphide
Time
Ag2
S
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Variable thickness with an average of 14 µm
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BSI of silver, copper and sulphur
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Combination of Ag, Cu, O and S onthe original
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Goal for Experiments
• Reproducing the effect where a possiblecomprehension of the exfoliation takesplace.
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Reproduction (15x annealed, not worked, 925/1000)
Thickness pure Ag of 6-8µmEnrichment of silver layer Enriched Ag/Cu
oxidelayer 16-20 µm
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EDS-Mapping925/1000 Ag15x annealed, not worked
Ag Cu O10 µm 10 µm 10 µm
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Conclusions
• Tarnished silver exfoliates at an average thickness of 14 µm
• Exfoliation takes place after handling the object• Coppersulphides and copperoxides stay behind• Bonded coppercorrosion slows down the
tarnishing• A direct relation between manufacturing
technique and tarnishing is evident
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Past, Present and Future
De-lamination of mercurygilded silver objects
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The Object with surface unclear
History of Technology and History of Art
Materials Science and analytical equipment
Conservation Science and understanding previous
treatments
Workmanship and manufacturing techniques
Reproductions showing the effects of the expected decay
or original surface
A better understanding of the object with it 's surface
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De-lamination of Mercury GildedSilver
Mercury gilding and history• Earliest known use by Chinese 300 BD• Widely used afterwards in Western Europe (treatises)• Based on a mixture of mercury and gold on top of a
silver alloy
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Gold and Mercury
The amalgam is made from pure gold and mercury.
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Amalgam is a paste
The mixture is appliedon the surface of the object, using brushes, and heated on a charcoal fire.
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Drops around the object
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Various silver objects with a mercury gilding
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100% Au
Ag/Cu alloy
(925 or 835/000)
Diffusion zone Au + Ag
Mercury gilding of silver according literature
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Reproduced mercury gilding
500 µm
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A mercury gilded silversurface is porous
BF DF
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A tarnished surfaceas result
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Delaminatedsurfaces
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Samples of objects
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Materials Science
Crossection and morphology
Even thickness of silver and gold Channel and island effect
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Boundary, between Au/Ag
Kirkendalleffect
Porosity behind the boundary
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Aim
Reproducing the effect of de-laminated mercury gilding
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Experiments and reproductions
• Pure gold on silver• Heating silver alloy at approx 350°C
and 700°C• Reproduction of mercury gilded silver
according a treatise• Exposing the reproductions to the
suspected effects
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Reproduction of pure gold on silver without mercury
or copper
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Diffusion of gold and silverwithout mercury or copper
(320 °C, 15,5 hrs)
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Diffusion of gold in silver at highertemperatures
(660ºC, 15.5 hours)
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Comparison of different morphology surfaces
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History of Technologyand workmanship
Al het zilverwerk dat men wil vergulden moet eerst witgekookt, en schoon gekrest zijn…
100% Au
≅ 100% Ag
Ag/Cu alloy
(925 or 835/000)
Diffusion zone Au + Ag
Mercury gilding silver according Van Laer's
handbook (1721, 1730 and 1768)
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Reproduction of silver(15x annealed, not worked, 925/1000)
Thick pure Ag of 6-8µmEnrichment of silver layer Enriched Ag/Cu
oxidelayer 16-20 µm
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Porosity grows due to loss of Ag, Cu oxides do not diffuse into the gold
Heating 760oC for 2 minutes
Ag ↑Ag diffuses in Au↑
Ag ↑ Ag ↑
AuAu does not diffuse back into Ag
Ag ↑
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Cu oxides present
Pealing offdelaminatedsurface
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Reproduction of silver(15x annealed, not worked, 925/1000)
Thick pure Ag of 6-8µmEnrichment of silver layer Enriched Ag/Cu
oxidelayer 16-20 µm
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EDS-Mapping925/1000 Ag15x annealed, not worked
Ag Cu O10 µm 10 µm 10 µm
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SEM images of original and reproduction
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Time-Temperature diagram of Ag in Au diffusion
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Time-Temperature diagram of Ag in Au diffusion
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Conservation Science
• What possible treatments could have taken place in the past that influence the current appearance?
• What possible treatments should takeplace in order to prevent further loss?
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Green corrosion
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Recognizing previoustreatments
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Conclusions
• Heating the mercury gilded silver object after manufacturing will result in loss of material.
• The temperature used for brazing is sufficient for a Kirkendall effect to take place
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Further and ongoing research
• Influence of galvanic applied gold layersand possible differences in diffusion
• Which method should be used for cleaning
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We know everything of the conservation of silver
Everybody can polish silver..
Everybody can polish silver..
Everybody can polish silver..
Everybody can polish silver..
Evereybody can polish silver..
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Silver saltcellars
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Saltcellar Claes Claesz Schoon
Amsterdam 1668 (BK-1957-15B)
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In detail
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Microcracks in the surface
(Magn: 40x)
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Conclusion
• Chemical cleaning will cause problems• Microscopic research with every object
before treatment
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Conservation of historic silver
• The object is in a showcase
• The object will beexhibited outside a showcase
• The object is in storage
Rijksmuseum, 1927
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Silver on display
• The showcase should be closed and contain no materials which can give off S (given tests are the Azide test and the accelerated aging test)
• If the showcase has an opening of 1 mm2 the exchange rate will be …… thus the outside environment will be exchanged x times a day
• The showcase should be made of safetyglass (which can have its disadvantages as well)
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Disadvantages of safetyglass (no outside reflection was allowed to take place)
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Silver objects outside a showcaseThe possibilities for conservation are:
Doing nothing• Advantage: beautiful
lustre if the H2S concentration is low
• Disadvantage: H2S concentrations are neverthat low, meaningcleaning many times and therefore loss of material
• Conclusion: it is better tolacquer the object
Lacquering the object withthree possible methods, dipping, brushing, and spraying. The lacquerwhich is most suitable is a nitrocellulose lacquer, ercalene or frigilene
How do we remove the lacquer?
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Dipping a lacquerUntil 1995 all silver objects in the Rijksmuseum
were dipped in frigilene (nitrocellulose lacquer).• Advantage: the whole object is covered with
lacquer• Disadvantage: crevices are filled with lacquer
which become hard to remove. An iridescentcurtain effect is in many cases the result. Because of slow evaporation of the solvent; dripping is visible.
• Conclusion: the layer of lacquer is too thick, therefore the iridescence is disturbing
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Iridescent curtain effect
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A lacquered object
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Brushing the lacquer
Various museums around the world brushlacquer their objects
• Advantage: a fume hood is enough forsafety
• Disadvantage: if one spot is missed, accelerated corrosion will take place, turning part of the object specifically black
• Conclusion: it is better to spray lacquer
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Accelerated tarnishing
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Spray lacquering the objectAll silver objects in the National Maritime Museum,
London are spray lacquered with frigilene.• Advantage: the chances for obtaining a better
covering are much larger, no brushstrokes are visible
• Disadvantages: practice is needed to do itproperly and a special fume exhaust is needed.
• Conlcusion: the best way to lacquer your silver, there are always companies who can do this foryou
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Conservation of silver at the Rijksmuseum
• 1240 objects on display• 2117 objects in storage
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Keep it from it from tarnishing
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The costs
• ArchiPress Pouches 100 pieces (27 x 41cm) 90,53 euro
• ArchiPress Pouches 100 pieces (28 x 50 cm) 155,83 euro
• Sealdevice 1.430,- euro
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Labour
• 5 minutes at 28 hours is approx. 7 weeks..
• But 2 minutes at 28 hours is approx. 3 weeks
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Result
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New showcases
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And than cleaned..