Artificial patination

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Dieses Buch handelt in Wort und Bild vom traditionellen Metallhandwerk, das die Schöpfer religiöser buddhistischer Statuen in Nepal seit über 1000 Jahren ausüben. Die kunsthandwerklichen Fertigkeiten werden mit grossem Bewusstsein für die Tradition gepflegt – sowohl in religiöser und ikonographischer als auch in technologischer Hinsicht. Die der Volksgruppe der Newar angehörenden Spezialisten sind Wachsmodelleure, Formenbauer, Giesser, Ziseleure und Feuervergolder. Ihre Arbeit zeichnet sich – teilweise bis heute – durch eine innige Mischung aus uralter Technologie, grossem Geschick, Religiosität und Kontemplation aus.

Bücher und Ausstellungskataloge zur buddhistischen Religion, Kunst und Ikonographie gibt es sehr viele. Zum handwerklichen Aspekt der Künstler, welche die religiösen Bildnisse im Metallguss schaffen, fehlte jedoch eine umfassende Dokumentation mit einem historischen Rückblick auf die Entwicklung dieser «archaischen» Technologien. Der fundierte Text und der umfangreiche Bildteil stellen die einzige aktuelle und komplette Dokumentation eines wohl aussterbenden, 1300 Jahre alten Kunsthandwerks dar: der «rituellen» Herstellung von buddhistischen Statuen im cire-perdue-Guss («Wachsausschmelz-
verfahren»).

Der Autor Dr. Alex R. Furger ist Archäologe und erforscht seit vier Jahrzehnten die antike Metallurgie und alte metallverarbeitende Techniken. Während 25 Jahren hat er die Römerstadt Augusta Raurica geleitet und lebt in Basel (Schweiz). Er ist Autor von über 130 Artikeln in Fachzeitschriften und zwölf kulturgeschichtlichen Büchern. Für die Feldstudien zu diesem Band war er wiederholt in Nepal und hat dort Dutzende von Kunsthandwerkern in ihren Werkstätten besucht und befragt.

The presented work primarily focuses on both the damascene
and patination technique which are archaeometallurgically
treated within the framework of the Bronze Age
north of the Alps. The aspect of patination is here perceived
as a pure artificial procedure. On the one hand the investigation
should reveal how damascenings were realized on
bronze objects and if the observations provide evidence for
clarifying the provenance of the rarely used inlay technique
– a major question that is still unsolved. On the other hand
authentic methods are to be examined in detail that once
presumably allowed the patination of prehistoric damascened
items for enhancing the weak color contrasts between
base metals and inlays.
First of all the study shows that metal inserts were not
used frequently throughout the whole Bronze Age and in
the different areas north of the Alps. There were longer
gaps between the various stages of the era. In contrast platings
as a special form of damascening (»surface damascening
«) were applied continuously since period Montelius
II, yet this decoration is only a characteristic feature for the
Nordic circle that was not adopted in southern regions.
Using only electron as decoration metal throughout the
entire Bronze Age platings differ from damascenings with
metal inlays (»inlaid damascening«) in another point that
besides gold or electron they mainly availed of unalloyed
copper. Later the spectrum of inlaid damascenings was
enlarged by pewter, bronze, and iron. The investigation
demonstrates furthermore that the cavities for inlays on
most objects were already designed prior casting. However,
multiple evidence is found for reworking cast grooves. Only
in some cases the grooves were made exclusively by chasing
or engraving.
For Late Bronze Age artifacts it becomes clear on account
of stylistic and technical characteristics that the metal inlay
technique was practiced only by few workshops, nevertheless
probably having influenced each other. Such considerations
are much more difficult to proof for the Early and
Middle Bronze Age as there are less damascened pieces. Yet,
similar decoration patterns and techniques suggest interactions
between single craftsmen or workshops. Unfortunately,
the provenance of the damascene technique still
remains unclear despite this new investigation. Though, it
is at least unlikely that the polychrome decoration was
directly adopted from Mediterranean or even Greek prototypes,
but the stimulations rather have to be searched in the
Carpathian region. Finally, also a selfcontained development
somewhere in Central or Northern Europe cannot be
completely ruled out.
On the basis of patination experiments it can be shown
that in fact human urine is suitable for coloration of damascened
objects with copper inlays. Ideally, the medium produces
purple-black patinas on unalloyed copper while the
addition of elements such as tin or arsenic to copper gives
somewhat lighter appearances. High concentrations of tin
result in light yellow or slightly green-gray coatings. Even
these colors may have been desired in prehistory on tin
bronzes as they perfectly contrast with purple-blackish
patinated copper inlays. The investigated method therefore
emerges as a possible and formerly neglected way for patinating
many damascenings of the Bronze Age north of the
Alps. For this, however, some preconditions have to be fulfilled
which are discussed in detail in the following work.

Over the past century, the powerful but mythical image of knights in shining armour, with bright polished swords to match, has dominated our view of what ironwork looked like: that of a polished greyish-white metal. This impression is gained not only from descriptions and illustrations in many books but is also obvious from even a casual walk around museum collections specializing in high status ironwork (such as the Royal Armouries in Leeds). But a close examination of much of this ironwork is likely to reveal that this was not its original appearance. Many poorly preserved patinated surfaces have been mistakenly removed by restorers and conservators wishing to improve the appearance of the objects in their care, not realizing they were altering the appearance by removing surviving traces of the original surface. However, it is possible to work out what much early iron or steelwork was originally intended to look like even if very little of the original surfaces survive. This can be done by the study of a combination of things: actual surviving traces, related decorative features (such as inlays), early descriptions, pictures, and even the use of inhomogeneous metal for certain objects or the making of composite ferrous artifacts. From this we can start to find out that much ironwork was actually intended to be either one or more colors, mostly in the range black (hence blacksmith) or dark grey to brown or blue, sometimes with one color intended to show up in contrast to another, or to a decorative feature such as an inlay. The probability that induced patination on iron surfaces was also intended to serve as a protective film is also indicated by some written sources. These issues need to be examined to promote a much better understanding of this little understood aspect of early ferrous metalwork, both to find out how and why it was intended to look originally and avoid bad decisions on how it should be cared for and displayed.

This paper presents an overview of techniques employed in antiquity-in different regions and at different times-for decorating metals by plating or applying surface treatments. Quite often the intention was to disguise metals and alloys to give the impression of better-quality materials. In other cases, the treatments produced special decorative effects and unusual colors. This paper deals with plating with gold and silver, various methods of gilding and silvering, depletion of gold and silver, and different kinds of artificial patination on various copper-based alloys. The best-known artificially patinated alloys are certainly shakudo-type alloys-that is, black-patinated copper-based alloys containing small amounts of gold and often silver and other metals. These alloys are inlaid with precious metals of contrasting colors and have been discovered in various archaeological contexts and historical times. Several other patinated alloys of various colors, including red, yellow, brown, orange, and olive, often rather similar to Japanese irogane (the word means "colored metal "), have been identified in recent times. The ancient methods of patination of iron will be briefly discussed. Ancient texts related to surface treatments will be commented upon.

Abstract
This paper discusses the methods employed to achieve polychromy on metals in Classical times, the ancient textual sources that give indications on how this was done in different periods, and shortly refers to the meaning of the variously coloured metals in antiquity. The first topic in this text relates the ways in which gold was applied on silver and copper-based metals: the mechanical application of gold sheet and foil, leaf gilding, mercury gilding and lead gilding. The paragraphs dedicated to silvery metals comprise silver foil, surface treatments on debased silver, arsenic-rich alloys, incoctilia and tinning. Some experiments that have been carried out on the iridescent copper-based alloy pyropus, mentioned by various Latin authors, but never identified up to now are then described. Artificially patinated alloys, such as the purple-black alloy Corinthium aes containing small amounts of gold and silver, but also red, orange and yellow patinated alloys recently identified on Roman and Romano-Egyptian objects conclude the essay.

Geometrical, ornamental and pictorial decorations are to be
found on a variety of metal objects of the Early Bronze Age
north of the Alps. They were applied to the objects by means
of various techniques, mostly to enhance their visual appearance.
Besides frequently used decorating techniques, there
are also those which are considered exotic in the metallurgical
industries of the middle, west and north-European Bronze
Age as they are only represented by few finds or their actual
use of the technique is even open to question. Amongst these
are the decorating techniques of damascening, patination
and arsenation; the last two named processes were used to
change the colour of the surface.
Starting with the Nebra hoard and further Early Bronze
Age objects, these techniques have been investigated by experimental
and archaeo-metallurgical research. The aim is to
reconstruct their application and artistic use. Especially
important knowledge has been gained about the technique of
damascening. The technical possibilities for the application
of Bronze Age patination can be gained experimentally, but
they cannot be necessarily proved on objects themselves. The
same applies to arsenation. On the other hand it becomes
clear that many linear decoration schemes on Bronze Age
objects are created by chasing and not through casting or
engraving.

This paper deals with the term ‘patina’ and the difficulty in defining a priori those materials that should be preserved on a metal surface. Dogmatic and restrictive ideas exist that only patinas, understood as visually pleasant corrosion, should be preserved. This has resulted in treatment criteria that have promoted the loss of important technological, historical and aesthetic information and materials. These comments arise from observation of damage to the sculpture of the Spanish king Carlos IV, known as El Caballito, in Mexico due to a non- professional treatment that caused losses to its surface. This paper proposes the term ‘surface layer’ to identify, describe and assess all materials on a metal surface, especially metal sculptures, irrespective of their nature, intention, origin, temporality or function. The term encourages the understanding that different materials on a metallic surface can be worthy of preservation, even if they do not correspond to a patina.

Over the last two decades, together with the increasing prices in the antique market and the proliferation of private ‘hobby collectors’, the number of fakes in circulation among antique shops, auctions and even institutions and museums has noticeably increased. So called ‘bronzes’ seem to be the favourite objects for both fakers and inexperienced collectors. In some cases the fakes are well made, so that often the professional can be fooled by them also. In this paper some examples of modern and ancient fake objects will be discussed.

Artificially black patinated objects from Mycenaean contexts are among the most interesting metal finds from the Bronze Age in the Eastern Mediterranean, however only a few examples have been scientifically examined, and there is some confusion among archaeologists on the nature of this metalwork. The inlays on Mycenaean bronze daggers and silver cups consist of a Cu alloy (kuwano in Mycenaean) containing low amounts of precious metals. After a surface treatment the alloy is patinated by different methods: the red-hot object is plunged into an aqueous solution with copper salts and alum or it is heated in the boiling solution. Material and technology are almost identical to those of Japanese shakudo. In this study the characteristics of the black patina on a Mycenaean dagger and silver cup are investigated and discussed.

Very special black patinated alloys were employed
in the western ancient world for exceptionally
precious objects. After the fall of the Roman Empire
they were lost and forgotten in the West, but they
survived in Asia. In Southern China they are known
as wu tong. The same material is called shakudo in
Japan, where it is considered characteristic of Japanese
metal art. Related patinated alloys of different colours
were employed in Roman Egypt and are found in
19th century Japan too. This paper will explore the
possibility of and means of technology transfer
from Egypt to Asia by examining the appearance,
composition, manufacture and characteristics of the various finds from the earliest to the latest in their historical contexts.

Recent analyses identified striking similarities in the production technique of objects with polychrome decoration, found
in various regions of the Roman Empire. The choice of coloured alloys employed for the inlays, the technical details and
the motives of the decorative figures represented on the magnificent artifacts indicate a Romano-Egyptian provenance.
The similarities are too marked to be casual and with all probability they testify to production from one and the same workshop.
In this paper the unusual patinated alloys of the inlays identified on the artifacts are illustrated and compared with
several ancient recipes.
Key words: artificial patination, polychromy, inlays, Roman Egypt

As scientific sub-project of research unit FOR550, module NW1 addressed the aesthetic factors of Bronze Age metal objects and their ornamentation. In addition to widely distributed decorative techniques like chasing and engraving, less frequently occurring techniques were also examined in detail. On the basis of the Nebra Sky Disc and its associated finds from the hoard, the aspects of damascening and artificial corrosion (patina) were for the first time ever discussed in sufficient depth. Research on a large part of inlaid Bronze Age artefacts as well as experiments provided new insights into the practice of metal inlaying (damascening) and its temporal and spatial development in Europe north of the Alps. Corrosion experiments with urine impressively showed how colour contrasts of damascened objects could easily be increased by creating polychrome corrosion layers. Furthermore, typical Bronze Age metal alloys were classified by hardness and colour to obtain clues as to why they were used. The contribution ends with the investigations of arsenic-rich surface layers on arsenical copper artefacts and their possible intentional creation.

The  practice  of  lithic  heat  treatment  creates  a  combination  of  initial  dull  flake  scars  and  subsequent smooth flake scars when the implement is finished after heating. Experiments were done to test  the  susceptibility  of  dull  and  smooth  flake  scars  to  etching.  The  points  were  etched  in  40%  hydrofluoric acid for either 40 or 60 seconds. In the 40 seconds experiment, the smooth flake scars of 9  (out  of  25)  heated  points  showed  less  etching  than  the  dull  flake  scars  or  no  etching  at  all.  These  artefacts formed a weathering pattern that is similar to double patina in reworked flints. Ten unheated control  samples  did  not  form  differential  weathering  between  different  generations  of  flake  scars.  In  the 60 seconds experiment 4 (out of 25) heated points showed some parts of the smooth surface to be less  affected.  Ten  unheated  control  samples  did  not  form  differential  weathering.  The  experiments  show that sometimes smooth flake scars are more resistant to etching initially. In  Scanning  Electron  Microscopy,  flint  artefacts  are  sometimes  pre-treated  with  hydrofluoric  acid.  Heat  treated  flints  are  susceptible  to  differential  weathering  by  hydrofluoric  acid.  Thus,  pre-treatment with hydrofluoric acid of heat treated SEM samples can lead to surfaces that are etched to a different extent.The  chemical  etching  in  this  study  does  not  replicate  any  natural  patination  process.  How  heat  treated  lithics  respond  to  natural  weathering  processes  cannot  be  predicted.  Further  studies  should  produce natural patination and test selected artefacts in contexts of intentional heat treatment for signs of heating.

The use of artificial patination techniques in antiquity for deliberately changing the colours of metals through the production of corrosion layers on the surface, has been strongly discussed for many decades. However, until now there is only evidence for such practices from ancient Egypt, the Mycenaeans and the Roman period. The present paper therefore shows for the first time that thermal treatment was intentionally used for artificial patination in Late Bronze Age Europe. This is illustrated on a supposed Italian winged axe using a combination of scientific techniques. The analysis shows the aesthetical intention of the craftspeople, as it can be clearly demonstrated that a strong colour contrast was favoured. The object is therefore not only the earliest example illustrating this kind of patination technique but also testifies the selective use of metallurgical knowledge on the cusp of the Early Iron Age. It further opens the possibility that colour treatment of European metal artefacts was more common in non-classical antiquity than has previously been thought.

During conservation of ten Burmese lime boxes in the British Museum, problems with patina were noted. One of the used materials is mylar, a black patinated copper alloy. Partial removal of surface dirt, or a wax layer, was thought to affect the appearance of the patina. In addition, XRF analysis showed that on some 'copper' boxes the metal was in fact mylar suggesting it had originally been patinated. To investigate patination techniques and options for conservation, fourteen different alloys were reproduced. Samples of these were used to test patination methods, stripping of patina, repatination and coating with wax. Optical microscopy, colour measurements and XRF analyses (x-ray fluorescence) were carried out. The method of patination by handling the metal is suggested to be most suitable for restoring the patina. However, specific conditions would be required to perform such a restoration on original material.

Direct evidence for the intentional patination of metal objects is difficult to ascertain and therefore studies concerning this technique are controversial. Only a couple of objects with artificially patinated surfaces have been positively identified, ranging in date from the early 2nd millennium BC to Roman and medieval times. In this paper a skilfully crafted and coloured Early Iron Age bronze axe belonging to the Villanova culture of ancient Italy was selected for examination. Optical microscopy and multiple mineralogical analyses of the surface of this object demonstrate that it was patinated deliberately by a thermal treatment technology (thermal patination). So far, this Iron Age axe is the oldest European object where this technology had been applied.

The main focus of this thesis is the scientific investigation and conservation of bronze fragments from an antique bed frame which are inlaid with silver and copper. They were found in a Roman palace in Avenches (Aventicum, VD). Their appearance today is the result of different events. It was produced in Roman times and used for approximately 200 years until it most likely got destroyed in a house fire. After burial, corrosion introduced other chemical changes to the surfaces of the objects.
The combination of different metals and alloys gave the surface a polychrome effect. However a polished surface would have resulted in only slight color contrast. Therefore it is likely that the contrast was artificially increased by patination of either the inlays or the surrounding metal.
Artificial darkening of copper alloys has been recorded in antiquity around the Mediterranean. Small quantities of gold or silver were added to the copper alloy that was then artificially oxidized to form a purple or black cuprite layer. The particular composition of these alloys makes it relatively easy to identify them. It has been found on objects from Greece, Egypt and the Middle East.
Written sources also show that various other methods of surface coloring were used in ancient times. However such superficially patinated surfaces are extremely difficult to identify on archaeological objects, as corrosion processes during burial often transform and replace them.
The aim of this study was to find evidence that could confirm the presence or absence of artificial surface coloring. In addition to the bed frame fragments, ten other objects from the collection of the Musée Romain Avenches were examined. Elementary analyses allowed the identification of all metals and alloys. Surfaces were investigated and documented by means of structural and elementary analyses. No clear evidence for artificial patination was found except for one bronze that was inlaid with a copper-gold-silver alloy that could be oxidized to a dark cuprite surface. Together with another object from Augst (Augusta Raurica), this is the second case in Switzerland that documents surface patination by the use of precious metals in copper alloys. Clues to a possible coloring with sulfur were found on one amulet. Half of the examined objects had the copper oxide tenorite on their surface, which results from exposure to high temperatures. Although patinas with artificially generated tenorite have been recorded in the past, this cannot be positively be confirmed for the objects from Avenches.
To obtain additional information about the nature and composition of the inlays and the surrounding metal, two samples were taken from a bed frame fragment. They were then embedded and polished. Elementary and structural analysis allowed the localization of the former „original surface“ through the presence of specific markers. The latter has been altered by the fire and replaced by corrosion products.
Through this analysis a well argued conservation plan for the bed frame fragments can now be proposed. This does not aim at revealing the original metallic color scheme (as has been done in the past with stripping methods), but at preserving a maximum of information and the original surface in its altered state.
Despite all intensive investigation, no clear conclusion can be made about the original appearance of the bed frame. The absence of gold and silver in the copper alloy excludes the possibility of a dark cuprite formation as observed on one of the other objects from Avenches. However an artificial darkening of surface components with sulfur or by other treatments (as urine for example) remains a possibility. In this case virtual media was used to illustrate the various possible color combinations.
This work confirmed that, today’s analytical methods cannot positively identify every kind of artificial patina on archaeological metals. Therefore deliberate surface coloring can remain unrecognized on many artifacts in museums. It is of outmost importance that potential information relating to past surface treatments is preserved for future analysis. The precise identification of the original surface and a minimal removal of corrosions products are essential when dealing with such artifacts.

Contributo al Convegno svoltosi in occasione del restauro della Vittoria alata di Brescia (Firenze 27-28 maggio 2019). Gli atti del Convegno sono stati pubblicati nel volume "Il restauro dei Grandi Bronzi : Laboratorio aperto per la Vittoria Alata di Brescia" a cura di A. Patera e F. Morandini, Centro Di, Firenze, 2020, pp. 73-79

In 2016, Terra Mare Conservation, LLC, was contracted by the City of Atlanta, Georgia, to undertake conservation of Cometh the Sun, a monumental sculpture fabricated in weathering steel by artist Curtis Patterson. The collaborative project involved conservators, metal fabricators, metal trades, city public art officials, and the artist. The sculpture has a combined weight of 5.7 tons, and is 15.2 meters in length, 6 meters in width, and 4.5 meters in height. Conservation efforts involved disassembly, replacement of 40 severely corroded areas of steel, artificial patination, sealing of moisture-prone areas, drainage enhancement through the installation of new anchors and footers and a concrete slab, and reassembly. Samples of the original weathering steel patina and new artificially patinated samples of A588 weathering steel were assessed by electrochemical impedance spectroscopy (EIS) using a gel-polymer electrolyte cell. Composition of the natural and artificial patinas was assessed by Raman spectroscopy, and thickness and color were measured. Analytical results demonstrated that the poor performance of the natural patina was not attributable to pollutants but to improper development in areas prone to water retention. These findings highlight the need to follow manufacturers’ specifications when using weathering steel to prevent failure of the protective patina.

La coppa di Enkomi, uno splendido recipiente in argento con decorazioni policrome in oro e nero, ora parte delle collezioni del Museo di Nicosia, Cipro (inv. nr. 4207), è stata rinvenuta durante gli scavi degli anni '40, condotti dalla missione francese ad Enkomi, e pubblicata da C. Schaeffer.  Il presente studio ha dimostrato che le decorazioni nere sulla coppa d'argento rinvenuta ad Enkomi da Claude Schaeffer non sono di niello (cioè di solfuri metallici di aspetto vetroso e fragili), ma si tratta invece di agemine in lamina a base di rame contenente piccole quantità di oro e di argento, patinata artificialmente per ottenere un colore nero, adatto a risaltare sull'argento dello sfondo. Le agemine in oro, sono a loro volta ageminate sulla lamina nera, secondo la tecnica nota da vari reperti micenei, come ad esempio i pugnali del museo di Atene.

The practice of lithic heat treatment creates a combination of initial dull flake scars and subsequent smooth flake scars when the implement is finished after heating. Experiments were done to test the susceptibility of dull and smooth flake scars to etching. The points were etched in 40% hydrofluoric acid for either 40 or 60 seconds. In the 40 seconds experiment, the smooth flake scars of 9 (out of 25) heated points showed less etching than the dull flake scars or no etching at all. These artefacts formed a weathering pattern that is similar to double patina in reworked flints. Ten unheated control samples did not form differential weathering between different generations of flake scars. In the 60 seconds experiment 4 (out of 25) heated points showed some parts of the smooth surface to be less affected. Ten unheated control samples did not form differential weathering. The experiments show that sometimes smooth flake scars are more resistant to etching initially. In Scanning Electr...

Abstract This paper presents an overview of techniques employed in antiquity—in different regions and at different times—for decorating metals by plating or applying surface treatments. Quite often the intention was to disguise metals and alloys to give the impression of better-quality materials. In other cases, the treatments produced special decorative effects and unusual colors. This paper deals with plating with gold and silver, various methods of gilding and silvering, depletion of gold and silver, and different kinds of artificial patination on various copper-based alloys. The best-known artificially patinated alloys are certainly shakudo-type alloys—that is, black-patinated copper-based alloys containing small amounts of gold and often silver and other metals. These alloys are inlaid with precious metals of contrasting colors and have been discovered in various archaeological contexts and historical times. Several other patinated alloys of various colors, including red, yellow, brown, orange, and olive, often rather similar to Japanese irogane (the word means “colored metal”), have been identified in recent times. The ancient methods of patination of iron will be briefly discussed. Ancient texts related to surface treatments will be commented upon.

Nota di restauro pubblicata sul bollettino annuale dell"Opificio delle Pietre Dure, dedicata allo studio e al restauro di un bronzo della Galleria d'arte Moderna di Palazzo Pitti (direzione tecnica del restauro: Agnoletti; restauratrici: Agnoletti, Baruffetti, Nesi, Bogdanova; direzione storico artistica: Speranza, Condemi; diagnostica: Cagnini, Galeotti, Porcinai), OPD n. 31, 2019, pp. 169-179

... Brian Gilmour a * & Alessandra Giumlia-Mair a pages 999-1006. ... A very similar case is that of another, slightly later, spearhead. It is an almost perfectly preserved Roman ceremonial spear or lance head recovered from the River Moselle at Trier, dated to the 4th century. ...

Im Fokus des Vortrages stehen die beiden Verzierungstechniken Tauschierung und Patinierung, die innerhalb eines bronzezeitlichen Gesamtrahmens und vor dem Hintergrund des Gebietes nördlich der Alpen behandelt werden. Hierbei wird einerseits durch archäometallurgische Methoden untersucht, wie und womit Tauschierungen (Metalleinlagen) an Bronzegegenständen technisch umgesetzt wurden und ob sich aus den gemachten Beobachtungen Aussagen bezüglich der Herkunft der seltenen Ziertechnik ableiten lassen. Andererseits zielt der Vortrag darauf ab, spezielle Methoden auszuloten, mit denen tauschierte Artefakte in der Bronzezeit zum Zweck der Kontraststeigerung patiniert, d. h. künstlich korrodiert worden sein könnten. Diesem Aspekt wird durch Korrosionsversuche im Labormaßstab sowie mit einer Reihe von analytischen Methoden gezielt nachgegangen.