Chap 6 : Tool marks
This section discusses and shows examples of the different types of tool marks that might be encountered on either the interior or exterior of a bronze sculpture, outlines working processes that can create tool marks, and focuses on how these marks may be identified and associated with a specific action. A flowchart summarizes the different possible tool marks [Fig. 495]
Features derived from the casting and fabrication process are discussed in Chapter 1
Since the external surface of a sculpture is more accessible than its internal surface, a large majority of the tool marks mentioned below will be found on the external surface; however, the internal surface may host a number of marks as well. If a mark is specific to an action associated with either the interior or exterior surfaces, its location will be indicated. Tool marks can derive from four different stages in the fabrication of a bronze: those made in the #{179} (s), those made in the mold, those made directly on the metal surface after casting, and those stemming from later intervention(s). Although technically similar to any other tool marks, inscriptions are treated as a separate feature [Fig. 495].
1. Tool marks made prior to casting
1.1. Tool marks made in the original model and/or in the #intermodel#
In creating the model (and possibly a wax #intermodel# for an indirectly cast sculpture), a variety of generic tools and/or those specific to a particular medium might be utilized that would appear on the external surface of the finished statue, whether the model be wax, wood, clay, plaster, stone, or another material ~See for example (Theophilus, Hawthorne, and Smith 1979): 135 describes the incising of his wax model. See also all the mar possible preparation of sockets for inlay (chapter 9)~. The fidelity with which these marks will be transferred to the cast metal surface will reflect the physical properties and composition of the investment or the mold, the #alloy#, the success of that particular casting, subsequent working of the surfaces, and possible later interventions.
| Most marks appear on the external surface of the finished statue. The only marks related to modeling which may be seen on the internal surface are those from tools used to work the interior surface of a hollow wax model and might include those from a brush or spatula. | {Fig. 138-153-158} |
1.2. Tool marks made in the mold
In indirect casting, the artist or founder has the opportunity to introduce additional details into the interior surface of the mold or to reinforce details not sufficiently well reproduced from the original model (see wax mold, investment mold, etc). How those marks are then transferred to the casting will depend upon the technique utilized. If a wax #intermodel# is created, the tool marks will be transferred to its surface with the artist then being able to assess the fidelity of the tooling with the option of further reworking. In sand casting, any alteration within the mold would be transferred directly to the casting (reference). In a method of bell-casting now used in England, the decoration designed to appear in relief on the exterior of the bell is created by punching the motifs into the interior surface of the loam cope (or outer mould) ~in reverse:In traditional bell casting, the decoration is added to the wax model of the bell, or to the clay false bell, and thereby translated into the inner surface of the cope or investment. references please~. The described marks can only appear on the external surface of the statue.
1.3. Tool marks made in the core
Marks made on the surface of the casting core will be transferred to the internal surface of the bronze statue (example of bell inscription -although a bit out of the range-to be added by Peta Motture). Some of the most common marks result from shaping or carving the core. Some of the most obvious examples would include the parallel lines associated with the shaping of a bell’s core on a lathe with the marks either from individual cutting tools or a strickle cut into the shape of the required form.
2. Marks of manufacture in the metal
After casting, the sculpture may be cold worked using a variety of tools to disguise manufacturing features, to sharpen and/or modify details translated from the model – some of which may not been sufficiently defined in the cast – and/or to decorate the surface. Distinguishing the specific nature of such tool marks, their purpose, and the time period of their introduction, ~can be difficult to discern:Edilberto Formigli provides a clear, useful and well illustrated review of tools and associated marks in his essay on Ghiberti’s doors of paradise @{8HTQAUD9}. See also, for example, (Vasari 1550), 165-66, section 68~.
When the casting is removed in its raw state from its mold or investment, it will retain remnants of its sprueing or gating system now filled with metal, together with scattered core pins, and possibly flaws such as flashes or casting defects [Fig. 3-25-110]. The multi-stepped process of removing or disguising such course features is known as fettling and might entail the use of saws, chisels, or coarse files (see Volume 1, Chapter 1 of the guidelines for casting and fabrication features and Volume 1, Chapter 4 on repairs). Flashing and casting defects may be present on the external surface as well as on the internal surface.
| The casting core is frequently removed after the casting, potentially leaving scratches or chisel marks on the internal surface of the statue. | {Fig. 122} |
1.2.3 To sharpen/enhance or decorate
The amount of work required to bring a casting to its finished state depends upon the quality of its #{13}. ~While it is possible that no significant finishing might be necessary:See, for example, (Vasari 1550 ditto see above), 166, section 69: ‘But that is a truly marvelous thing which is come to pass in our times, this mode of casting figures, large as well as small, so excellently that many masters made them come out of the cast quite clear so that they have not to be chased with tools, and as thin as the back of a knife.’ [Other refs for other periods than Renaissance would be welcome] See also (van Langh 2012: 77-103)~, more usually, the founder, #chaser#, or artist would finish all of the broadly modeled surfaces and ~introduce or reinforce details, textures, and patterns: Although not referring to sculpture, Theophilus describes the finishing of his cast censer in his 12th century treatises: After this, first file across all the grounds using various files, square, triangular, and round, then engrave them with engraving tools and scrape them with scrapers. Finally clean the work all over with sand and sticks whose ends are slightly shredded, and gild it. Similarly, in 1550 Vasari briefly describes how the workman finishes a bronze using, …burins, burnishers, chasing tools, punches, chisels and files…, to remove material, smooth down the overflow of metal, and, …with other tools that scrape, he shaves and cleans the whole of it diligently, and finally with pumice stone gives the last polish ((Vasari 1550): 165; see also, e.g., Gauricus 1504/Chastel and Klein 1969: 232-34 re chasing and finishing). See also sockets for inlays (chapter 9)~ [Fig. 75-94-95-154-191]. All evidence of such working would be restricted to the external surface.
The tools used to finish a cast surface can be divided into two broad groups – those that remove metal and those that compress metal. ~The former category includes files, chisels, gravers, burins, scorpers, scrapers, and abrasives while the latter would encompass hammers, tracers, planishers, grounders, matting tools, burnishers, and punches:(Untracht 1968) pp. 84-85; 111-113. See also (McGrath 2005)~. The number of variants within each group and tool type is limitless.
For broad, undecorated metal surfaces with a raw or porous structure, they might first be cut back with files [Fig. 14-133], chisels [Fig. 16], and scrapers [Fig. 27] before being compressed by #chasing# and burnishing [Fig. 30-75-94-95]. A final polish might then be achieved by a series of graded abrasives [Fig. 31].
Reliefs, designs or details such as strands of hair, eyelids, finger or toe nails may be reinforced, underscored, or highlighted by #chasing#, engraving, or chiseling [Fig. 1-132-160] 
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Decorative surface textures and finishes might be struck into the metal by punches and #matting# tools. |
{Fig. 94-95-96-154} |
The finishing of a sculpture’s surfaces might entail the use of a series of graded abrasives the scratches from which might be readily observable to the naked eye or microscopic. Until the introduction of sand papers, a variety of natural substances where used and might include shave grass, powdered stone, including roughing and sanding stone, sand paper, air abrasives (Andrew Lacey proposes to add a list – and maybe a diagram?).
1.3. Additional marks including inscriptions
Other marks may be have been added during the fabrication process to serve as assembly (figures needed) or registration marks [Fig. 131], as votive inscriptions [Fig. 156], or to identify an owner, commissioner, ~artist:It is not the scope of this section (nor of section 1.1 on molds and molding) to raise the issue around editeurs and signature of #{179} by artist to be translated into mould and associated problems of copyright, around life or posthumous casts, etc.~ [Fig. 66-71], or founder [Fig. 67-93-163]~:Barye’s Lions at the Porte des Lions, Louvre, provide an intriguing case of inscriptions. On the copy, the artist’s name has been chased (in the metal) by inverting the letters. In a short note (http://www.fontesdart.org/fontes-n100-elisabeth-lebon/), Elisabeth Lebon writes « Les deux Lions de la porte éponyme, sont tous deux signés de Barye, mais pas dans le même sens... En 1867, au moment de la reconstruction de la galerie, l'Etat propriétaire du bronze original acquis en 1847 pour le jardin des Tuileries décide, sans recueillir l'approbation de l'auteur, d'en faire exécuter une copie inversée pour orner l'entrée du passage avec la paire. Les différences de graphie montrent qu'il ne peut s'agir d'une inversion mécanique. En inversant sa signature, Barye cisela-t-il son mécontentement dans le bronze, à destination des observateurs attentifs des temps présent et futurs ? » (Lebon 2016) ProposesEnglish translation: « The two lions of the eponym gate (Louvre, Paris) are both signed by Barye but not in the same direction... In 1867, at the time of the reconstruction of the gallery, the State, as the owner of the original bronze, acquired in 1847 for the Tuileries garden decided to make an inverted copy in order to ornate the passage entrance and this, without the author’s consent. The differences in the graph attest that they do not result from just a mechanical inversion. In voluntarily inverting his signature, was Barye trying to chisel in the bronze his disapproval in a testimony to the careful observers for the present and future time?”.~[Fig. 69]. ~:V&A Le Sueur horse (inv#?) appears signed in metal; Antonio Susini apparently signed in wax prior to casting (figs and refs to be provided). EXAMPLES for other periods would be welcome (antiquity, asian and african art, etc) Warning! founder’s marks can change over time, can vary in style, and can include numbers.~
Inscriptions might be added either on the model(s) [Fig. 83-93] or the mold(s) prior to casting, or on the finished cast [Fig. 131-67-156], but, as with decorative marks, ~it is not always clear at what stage they were introduced:There are pieces that are known to have been signed by the artist in the model, mold, casting that might provide a means of differentiating the marks on other, less well known examples. Similarly, there are sculptures whose working is known – all in the model for instance – that can be used as a referent for comparison. PLEASE PROVIDE 1 or 2 examples for each~. Simple observations such as the erratic design of letters or their shallowness may suggest its cold working into the cast metal rather than its transfer from the softer material of the more easily incised model [Fig. 156]. To our knowledge, such marks are found principally on the external surface (any counter example?).
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A statue might have been reworked at a later date due to its being damaged or reinterpreted. The “re-use” of statues may be accompanied by a number of specific tool marks, including, for example, those left as a result of the removal of a statue from its initial position/base or scratches from the removal of inscriptions (example required). Ritual sculpture might undergo multiple alterations including repeated coating and deconsecration with the former obscuring original tooling and the latter generating new tool marks such as those associated with the removal of an attribute . |
{Fig. 85} |
Cleaning, polishing, and wear use can introduce scratch patterns and/or erode and etch the surface either in localized areas or across the entire surface [Fig. 174]~:Note that the study of wear on copper alloy artifacts is so far exclusively devoted to the understanding of the function of utilitarian objects rather than to the life of works of art. See (Dolfini and Crellin 2016)~. A variety of tool marks can be generated by intended or inadvertent damage to a sculpture and might include the marks from modern tools used to deface an object [Fig. 87] or to rework/reintegrate a blemished area.(more examples appreciated)
Marks on the surface might equally relate to deliberate actions such as technical examination. For instance, to identify an alloy or the generic type of the metal, a patina might have been scratched to reveal the metal below, a drilled sample might have been taken [Fig. 91], or a small incision made with a graver or scalpel to remove a sample.
Similarly, a sculpture’s patina may have been removed deliberately to repatinate the surface potentially destroying or affecting existing tool marks, as well as creating new ones. These marks may be found both on the internal and external surface.
Why investigate tool marks?
Frequently asked questions are listed below that may be addressed – at least partially – by investigating tool marks. The list may not be comprehensive (please add your questions).
2.1. Can tooling on the model be distinguished from cold working?
Usually, the tool marks made on the model prior to casting have a more fluid feel due to the relative ease with which the materials are worked (on a clay or wax model notably) with the edges then softened during casting as the more or less viscous liquid metal flows and solidifies [Fig. 5-7]. Under the microscope, it may be possible to observe that the mark retains its as-cast surface – see section 1.6.2.2 [Fig. 169].
| During cold working, significantly greater force is required to remove or deform the metal with the resulting mark having a more defined, sharper profile without any trace of an as-cast surface. | {Fig. 1} |
Additionally, marks made in the model might be deepened or reinforced in the metal potentially leaving traces of both operations still visible on the surface.
If decorative details on a part of a casting appear inaccessible to a tool, it suggests either they were created during modelling with the area in question worked as a separate element and then integrated into the whole [Fig. 165], or they were cast and finished prior to assembly.
When tool marks overlay work done after casting such as repairs, it is obvious that the decoration has been made or at least enhanced by cold working [Fig. 140-160].
Identifying the origins of a tool mark can be complicated by the fact that time, wear, and cleaning can erode the surface significantly smoothing or softening its details [Fig. 142](fig. 142, other image needed).
While it is beyond the scope of this paragraph to create a comprehensive list of how to distinguish between tooling made directly into the metal and that made on the model, all such details may help to characterize a tradition, a habit, a workshop, etc. ~that may in turn help to better document a bronze:For example, for the art of the Benin kingdom it does make sense to look at tool marks because before the colonial takeover in 1897 according to (Dark 1973), 50) chasing was mostly done in the wax, which allowed a high degree of finish and detail of design. So, it means that this distinction could tell us something about the age of the piece. Unfortunately though, the authors don’t know of any more recent examinations of this aspect.~.
2.2 Can as-cast surfaces be distinguished from cold worked surfaces?:
See van Langh 2012: 65-74 for a study of distinguishing cold worked from as-cast surfaces~
| In many instances, an #as-cast surface# will exhibit porosity, bumps, flashes, and other surface blemishes [Fig. 26]. The most efficient way to detect an #as-cast surface# is to find the associated surface imperfections (specific term to be found) that are often retained in areas of the casting that were difficult to access for subsequent tooling [Fig. 22] (for more, see chapter on casting defects). If there is visual access into the interior of the casting, one might be tempted to use those raw surfaces as an indication of what the exterior surface might have looked like; however, the composition of the core and investment often varied with each then imparting a different texture to the surface of the metal (this is irrespective of any surface finishing that might have been integrated into the model by tooling or imprinting from fabrics or other materials. Transitional areas on the bronze’s surface between different finishes or textures can retain tool marks associated with earlier steps in the finishing process not found in broader areas. | {Fig. 12} |
2.3 Can different types of cold working such as chasing and engraving marks be differentiated?
The cross section of a tool’s working face can help to characterize the kind of mark it might leave[d1] [R22] . Gravers, chisels, and scrapers have sharp cutting edges that are efficient at removing metal. Chasing tools, on the contrary, have rounded faces or blunt edges suitable for compressing metal. Depending upon the amount of metal to be removed, a V-shaped burin or graver might be held in the hand and a delicate line incised into the surface of the metal in one continuous cut leaving a tapering entry and exit mark [Fig. 167-168]. Increasing the depth of the cut might require that the graver be rocked back and forth creating a faceted quality to the line that can serve a decorative function as well. More depth yet might entail using a hammer with each successive strike eliciting a jump in the graver and a consequent step in the cut channel. As a line changes direction or turns to create an arc, the frequency of the strikes increases leaving a greater density of corresponding steps [Fig. 11]. Irrespective of the depth of the incised line, the tool creates a curl of metal at its cutting face. If the cut truncates abruptly, that curl will break off leaving a slight nub at the end of the cut [Fig. 9].
All chasing work is performed with the aid of a hammer. Generally, the tool is held perpendicular to the surface with each strike compressing the metal. The center of the tool mark is more concave than its edges. As for the graver, a number of strikes may be observed to follow a line [Fig. 160](fig. 160[pd3] ).
Warning: the final shape/aspect of the toolmark may strongly depend on the hardness of the alloy (D Robcis will provide images made with the same tracer on Hard copper/annealed copper/ brass/bronze). Also, toolmarks obscur and/or alter over time.
2.4 Can cold working and later intervention be distinguished?
Le bon sens....
2.5 In case of lost wax process, can one differentiate the wax model was made by the indirect or direct process?
Tool marks on the internal surface of the statue that pertain to the working of the wax (and not to the core nor to tooling after the casting) frequently testify for an indirect process [Fig. 138](fig. 138, other examples needed); however, the absence of tool marks does not preclude the use of an indirect model. That being said, some direct processes may also leave tool marks on the internal surface - a false core might be removed to provide access to the internal surface (Ghiberti Gates of paradise? Riccio horseman, Andrew Lacey’s productions). Warning: it may be difficult to distinguish between tool marks made in the wax, on the core, or in the metal when removing the core.
2.6 In case of lost wax process, can one find out whether the casting core has been made before the wax intermodel?
Tool marks on the internal surface of the statue that pertain to the working of the core (and not to the wax nor to tooling after the casting) clearly show that the core has been worked from outside and the wax applied afterwards, whatever the process. Such marks are rare [Fig. 136](fig. 136 comments and examples needed). Warning: it may be difficult to distinguish between tool marks made in the wax, on the core, or in the metal when removing the core.
2.7 Can different hands/craftsmen be distinguished?
Identifying the hand of a particular artist or workshop based on tool marks may constitute one ultimate goal for those investigating bronze sculpture. However, given the generic nature of both the tools and the techniques of surface working (with the possible exception of identifiable punches[d4] ),[LM5] this approach seems illusive. Moreover, ~one needs to bear in mind that several craftsmen may work on the same object:As an example, in contemporary brass casting workshops in Benin City, Nigeria, and Fumban, Cameroon there is a clear division of tasks and several individuals might be involved in the process. So, if the surface is worked, several individuals might have contributed and worked on one piece. The difference witnessed by Barbara Plankensteiner in 2002, 2004 and 2006 is that one single individual creates the wax model and therefore a hand might be identified based upon that.~. To date, there is no credible study on bronze sculpture effectively utilizing such information. Nevertheless, such a quest is only possible with the systematic cataloguing of all the working processes.
Surface metrology techniques may provide an appropriate methodology for documenting the repertoire of tools (see 2.5.3 below), particularly, those marks, such as the strike from a punch, that might be quite distinct and serve as a fingerprint or that might be characterized by a scar that would serve to identify it [Fig. 77-78-79]. It may also be possible to distinguish a chaser or engraver as being right or left handed.
2.8 Is it possible to estimate the overall technical aptitude of the craftsman?
Prehistorians and particularly those studying lithics have developed methods based on the statistical analysis of tool traces ~to quantify the technical ability of the craftsman:See notably the study of 280 engraved pieces of Magdalenian portable art ((Rivero 2016): traces considered as accidents or errors in the tracing were counted negatively, whereas others reflecting control of the tool and mastership in the use of various techniques were counted positively).~. The final objective is to try to assign different levels of experience in tool control and techniques; however, such methods need large and consistent corpuses.
How to investigate tool marks?
1 Visual exams and surface metrology
Tool marks are mostly of small dimensions often requiring magnification for their examination and characterization including classical stereomicroscopy, digital microscopy [Fig. 77-78-79-168-169], and electron microscopy that allows for large depth of field and very precise and user-friendly measurements (reference). Note that if the surface of the statue was painted or patinated (see section 1.8 on patina), that coating could have been reinforced or altered, possibly multiple times, thus hiding original tool marks. The surface of sculptures that have been buried might be covered by layers of passive and/or active corrosion products that can either hide tool marks or diminish their legibility. Under certain circumstances, it may be acceptable to do some selective cleaning to determine the nature of the tool marks. As already mentioned, details can also be softened by handling.
The use of specific light sources, including raking light and Reflectance Transformation Imaging [Fig. 191], may help to enhance the reading of the surface treatment.
An increasing number of approaches and techniques are being developed that enable the precise profiles of tool marks, their surface metrology, to be measured. Such details can be derived either by non-contact methods such as microscopy interferometry, and photogrammetry, or by contact methods such as profilometers. Some of the methods are limited to either horizontally oriented or planar surfaces. For more on these techniques, please refer to volume/section 2 (methods).
Silicone rubber impressions have been utilized to record surface metrology in numerous instances, ~including the examination of Qin bronze weapons:(Li et al. 2012)(Li et al. 2011). For other instances of the use of silicone to record tooled surface, see (Gwinnett and Gorelick 1998).~. The implementation of this technique to record tool marks on sculpture may offer further potential and future study. Analogous techniques used in other disciplines that could be applied to sculpture include technical studies of goldsmith’s work, bones and lithics @{C6DJAKIG}, ~as well as the forensic sciences:(Burd and Greene 1948), (Baldwin,David ; John Birkett, Owen Facey, Gilleon Rabey 2013)~.
3.2 Non-destructive techniques
| Radiography may be used whatever the source (X-rays, gammas, neutrons) and might help to detect tool marks not otherwise visible. Please refer to the general description of non-destructive techniques in volume 7. | {Fig. 63} |
3.3 Identification/measurement of stress
One avenue of research that may prove applicable to the study of surfaces is the identification/measurement by hardness testing, metallography and diffraction of metal stress due to cold working. The authors do not know of examples of such techniques being applied to investigate tool marks on bronze sculpture; however, micro hardness measurements (reference), and neutron diffraction have been utilized to find out whether the edges on protohistoric bronze axes were hammered and these experiments may serve as a potential example @{THJGJEGG}. Later intervention and even wear may induce stress. This may complicate the comparison of the relative stress associated with a cold worked surface as opposed to an as-cast surface initially stress-free.
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