A riveting past

Technical analysis of maiolica in the NGV Collection

At first glance these maiolica wares, beautifully decorated plates and jugs from centuries ago, appear deceptively simple in design and solidly sound. Looking beneath the surface, and closely at the manufacturing techniques, reveal an intriguing past that can be pieced back together.

In 2015 the NGV’s Collection of Italian maiolica wares was the subject of a comprehensive research project and subsequent publication.¹Timothy Wilson, Dunsmore, A., Strohschnieder, M., Italian Maiolica in the Collection of the National Gallery of Victoria, National Gallery of Victoria, Melbourne, 2015.

This included a detailed conservation study of a group of early utilitarian vessels through to later more refined wares of the Renaissance. A range of non-destructive examination techniques revealed some fascinating details. The first of these was X-radiography, which allows the conservator to collect information about the structural integrity and manufacturing techniques of works of art and is an important tool in assessing the condition of individual items. Another examination technique, x-ray fluorescence spectroscopy (XRF)²XRF involves the use of a targeted X-ray beam to produce spectra showing the elements present on the surface, was used to collect information about the glaze composition of a large number of the NGV’s maiolica wares, and in particular to verify the presence of tin. A third and complementary examination technique employed the use of ultraviolet light to study the surfaces of the maiolica wares. This technique takes advantage of the fact that certain organic materials fluoresce when exposed to ultraviolet light. It was used to locate repairs and overpaint on the surfaces of the maiolica wares, and to assess the extent of any repairs.

The observations and insights gained from the three non-destructive examination techniques were also compared with other international research using a range of scientific examination methods.

Italian maiolica wares – the clay body
Italian maiolica wares were typically made from a locally sourced light-coloured calcium rich clay, which resulted in a pale yellowish-buff colour after biscuit firing at 1000°C. The fired clay body was then covered with a lead tin glaze, decorated and fired a second time up to a temperature of about 950°C.

Examining the clay body
The NGV’s early utilitarian works from Orvieto form a distinct group. Compared to the later wares of the Renaissance, this group of vessels appear to have generally sustained much greater damage. This may be explained by the fact that these functional items were deemed useless once broken and, unless it was possible to mend the damage, would have been discarded. Unlike the Italian maiolica wares of the highly decorated type, which became collector’s items in their own time, these earlier, much more modestly decorated wares did not attract the attention of collectors until much later in the 1890’s. ³Kirsty Norman, ‘The Collecting, Restoring and Faking of “Archaic”Italian Maiolicas in the early 20th century’, in Alice B. Peaterakis (ed.), Glass, Ceramics and Related Materials: Interim Meeting of ICOM-CC Working Group, September 13-16, 1998, Vantaa, Finland, EVTEK Institute of Art and Design, Vantaa, 1998, pp. 134-43. Following this, broken vessels were repaired and often assembled from numerous shards, sometimes derived from multiple objects, as is the case with some NGV Collection items.⁴Only two of the NGV’s sixteen Orvieto jugs appear to be largely intact (3878-D3 not broken, 3880-D3 with loss in area of spout), all others have sustained substantial damage and have been repaired.

Repair techniques
Aside from the extent of damages, X-radiography has revealed useful information about historical repair methods and materials. It is known that a range of materials have been used in the repair of earthenware objects including bitumen, animal glues, plaster, lead, and iron rivets.⁵Wihr 1977, Williams 1988, Buys and Oakley 1996, Dooijes 2007, Dooiijes and Nieuwenhuyse 2007, Nieuwenhuyse 2008-2009 in Isabella Garachon, ‘From Mender to Restorer: Some Aspects of the History of Ceramic Repair’, in Hannelore Roemich (ed.), Glass and Ceramic Conservation 2010. Interim Meeting of the ICOM-CC Working Group, October 3-6, 2010, New York 2010, p. 23.
Stephen Koob, ‘Obsolete Fill Materials Found on Ceramics’, Journal of the American Institute for Conservation, vol. 37, no 1, 1998, pp. 49-67. It is also clear that certain repair materials were more suitable for utilitarian wares, if the aim was to use them again and the repaired item needed to be watertight and heat-resistant. This was achievable through mechanical repairs using riveting techniques. These techniques involved drilling into the object on each side of the break, either all the way through for lacing with wire or less deeply for insertion of d-shaped wire rivets (also called staples) across the break. The metal was typically brass or iron, and the rivets were often concealed either by in-painting or by filing a channel between the holes so that the metal could be inserted below the surface. X-radiography has revealed that five NGV Collection items have this type of repair, with either drill holes and/or rivets.⁶These are 4554-D3 and 4711-D3 (each with one rivet across crack), 4710-D3 (pairs of drill holes across cracks, no rivets remaining), 4708-D3 (several rivets and pairs of drill holes across several cracks), 4712-D3 (lots of metal rivets, possibly later repair). Still employed in China today, the use of metal wire for the repair of ceramics in China goes back at least to the 16th century,⁷Gallagher 1953, Thevenot 1666 in Isabella Garachon, p. 24. and in Western countries this technique is mentioned in historical sources as having been used in the repair of wooden bowls in Paris in the 13th century and in the repair of glassware in Germany from the 16th century.⁸Garachon 2010, Eggert and Straub 2009 in Garachon, p. 24.

While we cannot, with absolute certainty, date the rivet repairs observed in the NGV Collection items, it is curious that this repair method was not employed on any of the severely damaged utilitarian wares from Orvieto. We know, however, that these were not collected until around 1900 and that in all likelihood the repairs were associated with this period of collecting activity.

The rivet repairs observed on the 16th century maiolica plates are likely to be much older repairs than those undertaken on the Orvieto-type wares and are perhaps an indication that the plates were still ‘in use’ when the repairs were carried out. These more refined and painterly items of the Renaissance period had gained cultural significance at the time they were made. They were valued in aristocratic circles and often commissioned as gifts. One such example in the NGV’s Collection is the plate of Jupiter and Semele which is part of a service that was created in 1524 by Nicola da Urbino for Isabella d’Este.

X-radiograph showing rivet repair with drill holes arranged in pairs across the breaks. The metal rivets are no longer present.

This plate has been repaired across the lower section and the x-radiograph reveals an old rivet repair with drill holes aligned in pairs across the breaks. Undoubtedly the significance and value of such a plate would have warranted every effort to restore it. The careful execution of the repair is evident in the small size, minimal number and precise positioning of the drill holes at either end of the crack. Interestingly the holes have been drilled all the way through the earthenware wall, which would indicate that the broken pieces were tied together with wire instead of using wire rivets.

Another example of a rivet repair in the NGV Collection is the plate of Diana and Acteon.

X-radiograph showing extensive damage, with lengthy concentric crack running along the foot of the plate. Five broken sections have been previously repaired with rivets. Some metal rivets are no longer present.

Here metal rivets have been used to secure five broken pieces. In this case the holes have been drilled into the underside of the plate for insertion of the rivets, which have since been removed. A fairly large number of drill holes frame the cracks of this impressive plate, which measures 54.2cm in diameter and is almost double the size of the plate of Jupiter and Semele. Considering the large area of the damage, which extends over half the plate, a serious structural repair supporting the combined weight of the five broken pieces was necessary, thus explaining the large number of rivets used. This is a determined attempt to preserve a plate that had a discernible flaw in the glaze, and testimony to the appreciation and value attributed to this work at the time. The x-radiograph also shows a manufacturing fault in the clay body with a lengthy concentric crack running along the foot of the plate. This explains the flaw or crawling of the glaze in this area. The structural weakness caused by the crack would have presented a great risk when handling the plate – so much so, in fact, that it is reasonable to assume that the damage and subsequent repair date to the sixteenth or seventeenth century.

In comparison, the rivet repairs present in the plate Sacred Trigram are likely to be the result of a more modern, pre 1940 restoration. This is based on observations such as the absence of drill holes, the shape of the metal rivets is straight rather than u-shaped, and the fact that some of the rivets are passing through areas of loss that have fill material. This, and the fact that the rivets appear to have been made from the same metal wire, is evidence that all fragments were assembled at the same time.

X-radiograph revealing severe damage. The dish has been broken into thirty-three fragments and repaired with metal rivets. The rivets appear to have been made from the same wire and lack the typical U-shape that is seen in older repairs. The presence of rivets in the fill material suggests assembly of all fragments at the same time.

Ultraviolet light exposing the areas of repair (light-coloured areas). Large areas of overpaint are apparent on either side of the cracks (compare this with the x-radiograph above). Expert execution and painterly reconstruction of all the decorative elements present the dish in good condition when viewed in visible light, despite its extensive damage.

Italian maiolica wares – the glaze
A glaze is a glassy layer fused to a porous body for either practical or aesthetic reasons. In order to produce such a layer, a mixture of silica in the form of sand, flint, quartz and fluxes is heated to just below the melting point of the clay body. The role of lead is critical in bringing the firing temperature down, but it is also necessary to introduce some other base or flux (soda ash, potash, borax or lime) to prevent crystallisation of the glaze and make it more durable.⁹Harold E.Thorp 1969, Basic pottery for the student, Academy Editions, London, 1969, pp. 58-61. The process of glazing is complex. In addition to an understanding of the drying properties of the various clays and firing temperatures, it requires knowledge of glaze compositions to achieve a glaze that is a perfect fit for a particular clay body. The glaze ingredients of maiolica wares described by Cipriano Piccolpasso ¹⁰Cipriano Piccolpasso, The tree books of the potters art, trans. Ronald Lightbown & Alan Caiger-Smith, 2 vols, Scolar Press, London, 1980. include lead oxides, tin and marzacotto, which is silicate of potash made by fusing sand and calcined lees, are testament to an awareness at the time of practical implications of complex chemical processes.

Examining the glaze
While the advantages of tin as an opacifier had been known in the Islamic world since about 800 AD¹¹Alan Caiger-Smith, Tin-Glaze Pottery in Europe and the Islamic World. Faber, London, 1973., tin was not a local product in Italy and distribution was limited by the cost of importation, mostly from Cornwall, England. The tin-glaze technique is known to have spread through Italy by 1300, and a range of colours were added to the manganese purple-brown and copper greens of the early maiolica arcaica. After 1300 the modest palette was slowly extended by using imported cobalt for a deep blue, antimony for yellow, and iron to create a range of oranges. This progression is reflected in the NGV’s Collection of Italian maiolica wares, which includes some early maiolica arcaica through to some very fine examples of Renaissance maiolica wares.

A group of sixteen jugs from Orvieto and nearby is of particular interest as their manufacturing dates lie between 1200 and 1400. This coincides with the introduction and distribution of tin oxide in Italy and presents an opportunity to study the refinements of the glaze over time.

Glazes to which tin oxide has been added tend to be whiter than the lead alkali glazes, which appear more yellow in colour. Despite this, visual identification is made difficult by the fact that the appearance of glazed surfaces may vary depending on the colour of the clay body and the degree of weathering that individual items might have been exposed to. A reliable method for detecting the presence of tin in a glazed surface is X-ray fluorescence spectroscopy (XRF).¹²This non-destructive technique emits x-rays and the elements in the surface respond with characteristic x-ray fluorescent signals which are recorded in a spectrum. (Data collection: no filter no vac 60 sec 40 kv 3.20 uA). This non-destructive examination technique provides an instant ‘fingerprint’ of the elemental composition of material surfaces. Applied to the NGV’s Orvieto jugs, tin was detected in all but four jugs.¹³ These are 3884-D3,3872-D3,3870-D3 and 3880-D3. The absence of tin corresponds with an early manufacturing date of 1150 – 1300.¹⁴3871-D3 and 3883-D3 are also believed to have been made between 1200-1300, but do contain tin in their glaze.

Extent of repair
The extent of previous repairs is not always easy to determine. While x-radiography enables us to identify structural damage and the measures taken to rectify this, for example the metal rivets, cosmetic repairs and overpaints on the outer surface sometimes extend beyond the damage and obscure intact original surfaces. Examining surfaces with ultraviolet light, which causes certain organic materials to fluoresce, can assist in locating repairs on the outer surface and is an excellent non-destructive tool for quickly assessing an artwork’s condition. This technique has proven very useful in the examination of the group of Orvieto vessels in the NGV’s Collection. These have sustained considerable damage in the past and have been extensively repainted, including the decorative elements in filled areas.¹⁵All of the NGV’s early jugs from Orvieto have been bought at the Ridout sale in 1938, with twelve of sixteen jugs sold as part of lot 106. Images of five jugs are published in Honey, William Bowye, A Catalogue of the Collection of Italian and Other Maiolica Formed by William Ridout, privately printed, London, 1934. These show the condition before 1934 and are essentially in unchanged condition since. The repairs must therefore have been undertaken before 1934. A pharmacy jar (Acc.No 3868-D3), also bought at the Ridout sale in 1938, has undergone major repair with its base fully replaced. This pharmacy jar is also shown in Honey with the repair in place. A photograph from approximately 1910 of the same pharmacy jar with its original base is shown in Satolli Alberto (ed.), La ceramica orvietana del medioevo, exh. Cat., Milan, 1983 with the photo credit to Raffaelli-Armoni.

X-radiograph showing multiple breaks and larger losses at the top of the spout and and in the top and lower sections of the body.

Ultraviolet light showing the areas or repair (light coloured areas and mauve areas along edge of base and near spout), confirming at least two separate conservation treatments using different repair materials.

X-radiograph showing extensive damage, including partial loss of the spout and losses in the upper neck and on both sides. There is no evidence of metal wire or rivets.

A version of this essay was originally commissioned for and published in the publication Italian Maiolica in the Collection of the National Gallery of Victoria, National Gallery of Victoria, Melbourne, 2015.

Marika Strohschnieder is NGV Senior Conservator of Objects.

Notes