THE USE OF CYCLODODECANE AS A TEMPORARY BARRIER FOR WATER-SENSITIVE INK ON ARCHAEOLOGICAL CERAMICS DURING DESALINATION
VANESSA MUROS, & JOHN HIRX
ABSTRACT—This article discusses a preliminary study into the use of cyclododecane as a temporary barrier for the desalination of inscribed archaeological ceramics. Prior to desalination, pigmented or water-sensitive areas on ceramic objects are often consolidated with a resin. This process may alter the appearance of the object even after the resin has been removed. Cyclododecane, a volatile binder, has been used in the field of paper conservation for temporarily fixing water-sensitive media during aqueous treatments. This technique was adapted to conduct tests to determine whether water-sensitive media on archaeological materials could be temporarily protected with cyclododecane during desalination. Several marked modern terracotta samples were coated with cyclododecane using various application methods, and the samples were immersed or poulticed in tests simulating desalination. With the results obtained from these tests, an inscription on an Egyptian ostracon was coated with cyclododecane and desalinated. The results of the experiments and case study show that cyclododecane, when applied as a melt, offers considerable protection for water-sensitive ink during the desalination of archaeological ceramics and is a viable alternative to other materials commonly used for this purpose.
TITRE—L'utilisation du cyclododécane en tant que fixatif temporaire pour des encres solubles à l'eau lors du dessalement des céramiques archéologiques. RÉSUMÉ—Cet article présente une étude préliminaire sur l'utilisation du cyclododécane comme fixatif temporaire lors du dessalement de céramiques archéologiques avec dessins ou inscriptions. Préalablement au dessalement, la surface des céramiques sensibles à l'eau ou couvertes de pigments est fréquemment consolidée à l'aide d'une résine. Cette façon de faire risque d'altérer l'apparence de l'objet, même après que la résine ait été enlevée. Le cyclododécane, un liant volatile, a été utilisé dans le domaine de la restauration des œuvres sur papier comme fixatif temporaire lors du traitement des médias sensibles à l'eau. Cette technique a été adaptée afin d'effectuer des tests permettant de déterminer si des médias sensibles à l'eau pouvaient être temporairement protégés avec le cyclododécane lors du dessalement. Plusieurs fragments de terre cuite portant des inscriptions furent enduits avec du cyclododécane à l'aide de méthodes d'application variées, et les échantillons furent immergés ou traités à l'aide d'un cataplasme lors de tests simulant un dessalement. À l'aide des résultats provenant de ces tests, une inscription sur un ostracon égyptien fut recouverte avec du cyclododécane et l'objet ensuite dessalé. Les résultats de ces expériences et l'étude de cas démontrent que le cyclododécane, lorsqu'il est d'abord fondu et appliqué sur la surface, offre une très bonne protection pour les encres sensibles à l'eau lors du dessalement des céramiques archéologiques et constitue une alternative intéressante aux autres produits utilisés à cette fin.
TITULO—Estudio preliminar del uso del ciclododecano como barrera temporal de tintas sensibles al agua durante la desalinización de cerámicas. RESUMEN—Este artículo presenta un estudio preliminar del uso de ciclododecano como barrera temporal para la desalinización de cerámicas arqueológicas con inscripciones. Previo a la desalinización, los objetos de cerámica con áreas pigmentadas o sensibles al agua son, por lo general, consolidadas con resina. Este proceso puede alterar la apariencia del objeto, aún después de que la resina ha sido removida. El ciclododecano, un aglutinante volátil, ha sido utilizado en la conservación de papel para la fijación temporal de medios sensibles al agua durante tratamientos acuosos. Esta técnica fue adaptada para conducir pruebas y determinar si los medios sensibles al agua en materiales arqueológicos pueden ser temporalmente protegidos con ciclododecano durante la desalinización. Varias muestras de terracota moderna fueron recubiertas con ciclododecano utilizando distintos métodos de aplicación, y se sumergieron o se le aplicaron compresas para simular tratamientos de desalinización. Con los resultados obtenidos de estas pruebas, una inscripción de un ostracon egipcio fue recubierta con ciclododecano y desalinizada. Los resultados de los experimentos y estudios de casos muestran que el ciclodecano, cuando se aplica derretido, ofrece protección considerable para tintas sensibles al agua durante la desalinización de cerámicas arqueológicas, y es una alternativa viable a otros materiales que se utilizan comúnmente para estos fines.
TÍTULO—O uso de ciclododecano como proteção temporária para tintas sensíveis à água durante a dessalinização de cerâmicas arqueológicas. RESUMO—Este artigo examina um estudo preliminar sobre o uso de ciclododecano como proteção temporária durante o processo de dessalinização de cerâmicas arqueológicas com inscrições. Antes da dessalinização, as áreas pigmentadas ou sensíveis à água nos objectos cerâmicos são geralmente consolidadas com uma resina. Este processo pode alterar a aparência do objecto mesmo depois da resina ter sido removida. Ciclododecano, uma liga volátil, tem sido utilizado no campo da conservação de papel para fixar temporariamente os meios sensíveis à água durante os tratamentos aquosos. Esta técnica foi adaptada para a realização de testes a fim de determinar se os meios sensíveis à água em materiais arqueológicos poderiam ser temporariamente protegidos com ciclododecano durante a dessalinização. Várias amostras modernas de terracota marcada foram revestidas com ciclododecano usando distintos métodos de aplicação, e as amostras foram submersas ou foi-lhes aplicado um cataplasma, em testes simulando a dessalinização. Com os resultados obtidos nestes testes, uma inscrição num ostracão egípcio foi revestida com ciclododecano e dessalinizada. Os resultados das experiências e estudo de casos mostraram que o ciclododecano quando aplicado em estado derretido, oferece uma protecção considerável para as tintas sensíveis à água durante a dessalinização de cerâmicas arqueológicas e é uma alternativa viável em relação a outros materiais utilizados habitualmente com este objetivo.
The presence of soluble salts in porous materials is a problem frequently encountered by conservators treating archaeological objects. Because of their potential for damaging artifacts, the salts often have to be removed through desalination, whether by immersion, washing, or poulticing with water. This treatment can be problematic when the surface of the object is very fragile or when water-sensitive inks, pigments, or binders are present. In such instances, the surfaces of the artifacts have generally been consolidated, commonly with a resin, prior to desalination, to stabilize these areas (Strahan 1996; Koob 1991). Although consolidation may protect the object, it can sometimes alter the surface, making it dark or shiny, and can ultimately be difficult to completely remove after treatment.
Cyclododecane (CDD), a volatile binder, has been primarily used in conservation as a temporary consolidant, barrier, or fixative for a variety of materials during treatment or transport. It is cyclododecane's potential application as a fixative or hydrophobic barrier over water-sensitive materials such as inks, dyes, pigments, and binding media (Hangleiter 1998; Bandow 1999; Blüher et al. 1999; Brückle et al. 1999) that is the focus of this study. Research in the field of paper conservation in particular has shown the effectiveness of cyclododecane as a temporary fixative for ink on paper during washing. Not only have the hydrophobic properties of this material been useful in these aqueous treatments, but also the fact that it sublimes at room temperature ensures that the fixing is temporary.
For this study, the previous use of cyclododecane as a temporary fixative was modified for a series of tests that examined the effectiveness of the barrier produced in protecting water-sensitive ink on archaeological ceramics during desalination. The aim of this research was to examine the working properties of CDD and determine which films would protect the ink on modern terracotta samples during a mock desalination. The results of these tests would then be applied to the desalination of an Egyptian ostracon, an inscribed terracotta sherd (fig. 1). It is hoped that the research conducted will help in determining the viability and applicability of CDD as a material that can be used in the desalination of inscribed archaeological ceramics.
Ostracon before treatment, Egypt (333 B.C.E.–250 C.E.), terracotta, 11.7 x 12.1 cm, Los Angeles County Museum of Art, M.80.202.206
2 WORKING PROPERTIES OF CYCLODODECANE
Prior to beginning any of the tests on modern samples, the working properties of CDD were examined. Several published studies (Brückle et al. 1999; Hangleiter 1999; Stein et al. 2000) discuss the structure of formed films of CDD using different application methods and how the application methods affect the material's properties and behavior. Many of the published examinations and tests that examined CDD's working properties were repeated for this study (appendix 1), some with slight modifications, to ensure that the same results would be obtained using a different substrate or additional application methods. The results of these studies were used to determine the protocol for the bench tests on modern terracotta samples and to focus the testing on those application methods expected to produce the best protective barriers for the water-sensitive ink.
2.1 APPLICATION METHODS
Cyclododecane (C12H24) is a cyclic hydrocarbon that appears as a waxy solid. It has a melting temperature of 58–61°C (Jäegers and Jäegers 1999), and with low heat can be applied to surfaces as a melt. It is soluble in a range of nonpolar solvents, allowing it to be applied in solution. It can also be purchased as an aerosol spray (Hangleiter 1999).1 The application method used can affect the structure of the CDD films produced, which in turn affects the behavior of the film. It is important for conservators to be aware of the characteristics of CDD films in order to determine which application method will produce the most suitable film for the desired treatment and end result.
Previously published examinations (Brückle et al. 1999; Stein et al. 2000) have found that melting CDD on a glass slide produced a dense, compact layer of small acicular crystals. Solvent applications produced films with an open network of these crystals. The faster the solvent evaporated, the smaller and more tightly packed the crystalline structure formed. Added to the authors' examinations (fig. 2) was the aerosol spray film, which was made up of very small, slightly rounded crystals with spaces in between (appendix 1.1). From these evaluations it seems that the most effective, and least permeable, barrier would be made by those application methods that produce denser films with smaller crystals tightly packed together, such as the melt film or CDD in fast-evaporating solvent solutions. The spaces visible in some CDD solution-based films or the aerosol spray film may potentially allow water to permeate the CDD barrier and damage water-sensitive ink.
2.2 PENETRATION INTO POROUS SUBSTRATES
Tests have found that the application method can affect how deep CDD can penetrate into the substrate to which it is applied. Stein et al. (2000) learned that when comparing stone samples coated with cyclododecane as a melt and in solution, the solution tended to travel farther into the samples than the melt did. Warming samples prior to coating with molten CDD can help increase the depth of penetration
Crystalline structure of cyclododecane applied in various forms: (A) in petroleum ether, (B) in mineral spirits, (C) in dichloromethane, (D) in toluene, (E) as a melt, (F) as a spray (magnification 40x). Note how the slower-evaporating solvents, such as mineral spirits and toluene, formed long needlelike crystals with spaces in between each of them. Faster-evaporating solvents formed smaller crystals, in a tighter, less porous, crystal network. The melt appears to be made up of small crystals formed closely together creating a compact, dense film. The spray film seems to be comprised of small, globular crystals rather than acicular ones like the other films.
(Riedl and Hilbert 1998). Similar tests, after Stein et al. (2000), were conducted using terracotta samples to determine if a different substrate affected how far CDD penetrated. Unglazed terracotta samples, about 7 mm thick, were used for the tests. A 3 x 2 cm area on the surface of each sample was coated with CDD, as a melt using a heated spatula, in petroleum ether and the aerosol spray. To measure the depth to which CDD had penetrated into the sample, a “wettability test” was used (Kumar and Ginell 1997). After coating, the samples were cut in half, and the cross section was “wet” with a watersoluble dye. Colorhue Instant Set silk dyes were used as the indicator. Since cyclododecane is hydrophobic, the treated areas would not absorb the dye. The undyed section indicated the presence of cyclododecane and was then measured.
The results obtained were similar to those previously published (table 1). The aerosol spray, added to the authors' tests, appeared only to sit on the surface, and the depth of penetration could not be measured.
For the purposes of this study, the CDD would need to travel far enough into the sample to completely coat or encapsulate the inscription so that no damage could occur even from the action of water underneath, or behind, the inscribed area. Since the aerosol spray film appeared to sit on the surface, it was thought that this application method would not produce an adequate barrier because it would not coat the inscription sufficiently. CDD as a melt or in a solvent solution could be used since both seemed to penetrate deep enough into the samples to completely coat any ink on the surface.
2.3 SUBLIMATION RATE
The sublimation rate of CDD has been found to be greatly affected by the method of application used, in addition to factors such as the surrounding air temperature, humidity, and ventilation (Hiby 1997). In tests where limestone and sandstone samples were coated with cyclododecane, the coating formed from the melt took two to three times longer to sublime than those applied in solvent form (Stein et al. 2000).
Depth of Penetration of Cyclododecane (CDD), Applied in Various Forms, into Terracotta Samples
Examining the pore structure of plaster samples coated with CDD using a cryo-scanning electron microscope (SEM), Riedl and Hilbert (1998) found that a film of CDD from solution took five months to completely sublime, while the melt can take approximately nine months to completely sublime.
Sublimation tests similar to those conducted by Stein et al. (2000) were repeated applying CDD on glass slides and terracotta samples (appendix 1.2). The sublimation rate of the aerosol spray film was included in these tests. The authors' results were similar to those of the investigations discussed above (table 2). The aerosol spray film was the first to sublime, possibly due to its superficial penetration exposing it more to the air, and to its less dense film formation. The solutions were the next to sublime, where CDD in petroleum ether took longer to sublime than the mineral spirits solution. This is perhaps due to the differences in the formation of the solid films. The film produced by the melt took the longest to sublime because it forms as a very dense film of small, tightly packed crystals. In treatments that may occur over long periods of time, it is important to understand the sublimation rate of the application method chosen to ensure that the CDD film is not compromised.
Though cyclododecane sublimes over time, recent analyses have found that some residues can remain within the coated material (Caspi and Kaplan 2001). Using various analytical techniques, residues of materials chemically related or similar to cyclododecane have been found within ceramics and on the surfaces of glass slides. The residues appear to come from impurities in CDD as a result of the manufacturing process. Caspi and Kaplan also found that the
Rate of Sublimation of Cyclododecane, Applied in Various Forms, from Glass Slides and from Terracotta Samples
residues varied based on the manufacturer and the batch of CDD used. The conclusion drawn from these analyses was that the residues were present in such minute quantities and were chemically similar enough to CDD that they would not harm the object.
Tests were conducted by the authors to determine whether the batch of CDD used for these tests contained residues. Glass slides were coated with CDD as a melt, in various solutions and from the aerosol spray, based on the methodology of previous residue tests (Caspi and Kaplan 2001; Maish and Risser 2002). All slides exhibited white tidemarks after the sublimation of all the CDD films. Glass slides coated with only solvents also produced these tidemarks, likely due to impurities in the solvents. Therefore, the tidemarks seen on the slides are the result of impurities in the CDD and/or solvents, depending on the application method. Tidemarks like those seen on the slides were not visible on the surfaces of the terracotta samples coated for earlier examinations, but it is assumed residues are present within the samples. Testing and treatment using CDD will continue based on the conclusions of Caspi and Kaplan (2001). Future investigations and analysis, however, should be encouraged to further determine the effects of these residues, if any, on objects coated with cyclododecane.
3 TESTS USING MODERN TERRACOTTA SAMPLES
3.1 SAMPLE PREPARATION AND TESTING
Before CDD could be used for the desalination of the Egyptian osctracon, the material was tested on inscribed modern terracotta samples, in a variation of tests conducted by Brückle et al. (1999) of ink on paper. These tests would help to determine whether CDD would be effective at protecting water-sensitive ink during desalination and what application method would produce the best barrier. Based on the results of the examinations into CDD's working properties and published successful treatments, the melt and CDD in petroleum ether (PE) (90% w/v) would be the application methods used for testing.
Prior to coating, the terracotta samples were marked with ink of two varying water sensitivities. One set was marked with a Paper Mate nylon fiber point pen (ink no. 1), which seemed to be very sensitive to water. The other set was marked with Higgins Fountain Pen India nonwaterproof black ink (ink no. 2), which was less affected by water. In addition to their water sensitivity, the inks were also tested to see if they were sensitive to petroleum ether. Neither was affected by the application of the solvent. Each of the samples, measuring about 7 mm thick, was coated with a 0.05–1 mm film of CDD. None of the samples were warmed during application, and they were kept at room temperature during testing. An uncoated sample was included for each ink type to see the effect of the desalination techniques on the unprotected ink.
Two different desalination techniques were used for testing to determine if either had any effect on the behavior of the barrier films and inks. One set of samples from each ink type was immersed in deionized water, and another set was poulticed, using cotton wool and deionized water, both for 24 hours. The poultice material was applied to the back of the sample to easily observe any changes in the inscription. The inscriptions were examined at various intervals within a 24-hour period, after desalination and after sublimation of the CDD from the surface.
The CDD films were unable to completely protect the inscriptions marked with ink no. 1 (nylon fiber point pen) from damage (figs. 3, 4). The ink, whether coated by the melt or by petroleum ether solution, bled and faded. The extent of the damage observed was dependent more on the method of desalination used (table 3). The ink on the coated, immersed samples had a greater tendency to fade, while the ink on the poulticed samples was more likely to bleed. Cyclododecane proved to be ineffective at protecting this particular ink.
Cyclododecane, however, was very effective at protecting ink no. 2 (nonwaterproof India ink) during both poulticing and immersion (figs. 5, 6). While the inscription on the uncoated samples bled and faded, the
Terracotta samples marked with ink no. 1 (nylon fiber point pen) after soaking ([A] uncoated, [B] CDD in petroleum ether, [C] CDD as a melt)
Terracotta samples marked with ink no. 1 (nylon fiber point pen) after poulticing ([A] uncoated, [B] CDD in petroleum ether, [C] CDD as a melt)
Results of Tests on Modern Terracotta Samples Marked with Ink no. 1 (Paper Mate Nylon Fiber Point Pen) During Poulticing and Immersion
Terracotta samples marked with ink no. 2 (nonwaterproof India ink) after soaking ([A] uncoated, [B] CDD in petroleum ether, [C] CDD as a melt)
Terracotta samples marked with ink no. 2 (nonwaterproof India ink) after poulticing ([A] uncoated, [B] CDD in petroleum ether, [C] CDD as a melt)
coated samples changed very little. Although the differences between the samples coated with the melt and the PE solution were not substantial, there were differences in the time it took for changes to occur (table 4). It took much longer for the water to damage the inscription on the melt-coated sample than on the sample coated with the PE solution.
The results of these tests concur with the results of treatments using CDD on works of art on paper, where the melt was found to be a more effective barrier than the solutions during aqueous treatments (Bandow 1999; Brückle et al. 1999). Brückle et al. (1999) also found, as was the case with the two inks tested in this study, that CDD films differ in their effectiveness as a barrier according to the ink's degree of sensitivity to water. The films did not protect ink no. 1, despite the application method, because the ink seemed to be extremely sensitive to water. The CDD barriers better protected ink no. 2, which was less sensitive to water. These differences in the behavior of cyclododecane CDD on different types of inks suggest that some idea of a particular ink's sensitivity to water should be known prior to using CDD during any aqueous treatments. The water sensitivity of the ink on the ostracon will have to be determined prior to treatment to help reduce the risk of any damage to the inscription.
Surface examination of the samples, after sublimation of CDD from the surface, revealed a slight discoloration on areas that had been coated with cyclododecane. The surfaces coated with the melt appeared lighter than the rest of the sample. Under microscopic examination (10–40x magnification), these areas appeared rougher and more porous than the areas that were not coated with cyclododecane. Samples coated with the PE solution had darkened
Results of Tests on Modern Terracotta Samples Marked with Ink no. 2 (Higgins Fountain Pen India nonwaterproof black ink) During Poulticing and Immersion
or discolored on the areas coated. Microscopic examination did not show any significant change in the porosity or texture of the surface on these samples, as was seen with the melt application.
Since not all of the test samples exhibited these types of discoloration, other factors besides the application of CDD may be causing the surface changes. Because samples previously coated for earlier examinations, which were not soaked or poulticed, did not exhibit any surface changes, it is thought the discoloration or changes in surface texture may have been due to the dissolution of soluble material in the untreated areas of the terracotta samples during the mock desalination. Solvent residues or incomplete sublimation of CDD from the samples could also be factors in the discoloration. The cause and nature of the discoloration are areas that will need further investigation.
4 CASE STUDY: THE DESALINATION OF AN EGYPTIAN OSTRACON
Based on the results of the tests on modern inscribed ceramic samples, CDD was used in the treatment of an ancient Egyptian ostracon that required desalination. The ostracon, in the collection of the Los Angeles County Museum of Art, suffered from a soluble salt problem. Having been previously stored in an environment with fluctuating temperature and humidity, the salts continued to crystallize and deliquesce within the pore structure, causing subsequent damage to the object. The surface of the ostracon was slightly flaky and powdery, with salt crystals visible. The salt damage was resulting in the loss of material, but, more important, in the loss of the inscription. A decision was made to desalinate the object, but because the ink or binder used was likely to be water sensitive, the inscription had to be protected first. CDD was chosen for the barrier because, in contrast to resins, its volatility would allow the coating to be temporary, without altering the color or appearance of the surface. If, after desalination, further stabilization of the surface was needed, fragile areas could be treated locally, thus minimizing the addition of material to the object and changes to the surface. The melt application of CDD would be used because it seemed to produce a better barrier for ink during the mock desalination tests and was successful in other published treatments (Bandow 1999; Brückle et al. 1999).
Literature that discusses the writing of ancient Egypt (Forbes 1965; Singer et al. 1965) states that early inks were generally carbon black mixed with a binder, such as a gum or proteinaceous material, or in later periods an iron oxide–based material. In both cases, either the ink or the binder is considered water sensitive. A test was conducted to determine whether the ink, or binder, if present, was water sensitive. This test was also important because the age of the ink could cause it to behave differently than expected when in contact with water. To make these determinations, a small, disassociated flake with a small dot of ink was immersed in 30 ml of deionized water for 72 hours. The ink faded slightly upon immersion, but no other changes were observed. It was concluded that the ink was only slightly sensitive to water, and, therefore, based on earlier test results, the melt film should provide adequate protection for the inscription.
A sample of the wash water used to observe the ink's sensitivity to water was used to determine what soluble salts were present. Microchemical tests were conducted to identify the presence of three common soluble salts in the wash water: silver nitrate to identify chlorides, ferrous sulfate for nitrates, and barium chloride for sulfates (Buys and Oakley 1993). The tests gave positive readings for the presence of nitrate and chloride salts.
The CDD was melted on the surface of the ostracon using a Zephytronics Air Pencil ZT-2 (SMT Pin Point Soldering System), because it was felt the heated spatula, used for earlier tests, would apply too much pressure on the fragile surface. The air pencil was originally designed for soldering electronic and computer components, but it has been modified for use in conservation treatments, such as tape removal from paper (Stanley 1998). It melts or softens materials using warm air, where the air flow and temperature can be adjusted separately, as needed. The use of the air pencil would allow the cyclododecane to be melted using controllable warm air, without applying pressure to the object's surface. A low heat setting and the minimum airflow were used to melt the CDD on the ostracon. During application, pieces of solid cyclododecane were held just above the surface of the ostracon with tweezers. The air pencil was then held far enough away over the cyclododecane to allow the solid piece to melt, but not for the airflow to disturb any of the surface flakes. Only the area of the inscription was coated.
The ostracon was desalinated by poulticing because immersion would result in the displacement of any flakes on the surface. Cotton wool wadding, dampened with deionized water, was placed behind the ostracon, where the surface was more cohesive. Poulticing from the back allowed the inscription to be visible during treatment so that any changes could be easily observed. The poultice material was changed every 24 hours, and the salt content monitored by soaking the poultice in 250 ml of deionized water and measuring the resulting conductivity. The ostracon was kept in a covered tray and sealed in a polyethylene bag during treatment to prevent the sublimation of the coating, something that occurred on some of the poulticed terracotta samples during testing.
Desalination was completed after two months, when a series of similar conductivity readings were obtained within the acceptable level of 75–100 μS/cm (Buys and Oakley 1993) (fig. 7). The ostracon was left to dry out slowly in an open polyethylene bag, for about four to five weeks, until no cyclododecane remained on the surface and the inscription could be examined. Based on the sublimation rates from earlier tests, it is likely that some CDD remained within the ostracon and would require a few months to completely volatilize.
Examination of the surface and inscription after treatment showed no bleeding or fading of the ink (fig. 8). The inscription appeared clearer after desalination. Comparison of the inscription before and after treatment showed no loss of the characters (fig. 9). No tidemarks were left, and no discoloration of
Measurements of the conductivity of the poultice material wash water during desalination. Because the poultice could not be changed over the weekend, there were some increases in the conductivity readings the following Monday morning. Desalination was completed once the reading leveled off within the accepted conductivity levels of 75–100 μS/cm (Buys and Oakley 1993).
Ostracon after treatment (fig. 1)
the surface occurred in the area coated. The only visible change was the loss of two small flakes, visible in the before photograph and missing from the surface after treatment. These two flakes had only a small ink mark, and the markings were not discernible as a letter or character. The loss may not be associated with the fading of the ink due to the permeability of the cyclododecane film in that area, and more than likely was the result of loss during handling.
This study into the properties of cyclododecane has provided further insight into its hydrophobicity and a possible new use for this material in the treatment of archaeological objects. Adapting CDD's use as a temporary fixative for ink on art on paper during aqueous treatments, tests were developed and carried out to investigate the effectiveness of CDD as a temporary barrier for inscribed archaeological ceramics during desalination. Published examinations, and the authors' observations into the working properties of CDD, were used to define the parameters for a series of tests conducted on modern terracotta samples undergoing mock desalination. The samples tested, marked with two inks of different water sensitivities, showed that the application method used and the ink's sensitivity to water affected the behavior of the CDD film and how well the inscriptions were protected. The very water-sensitive ink was not protected by any of the CDD films. Both CDD in a petroleum ether solution and as a melt did create a better barrier for the less water-sensitive ink. The CDD melt film proved to be the most effective film in protecting inscriptions made with slightly water-sensitive ink from water damage during mock desalination. Based on these results, the desalination of an Egyptian ostracon was undertaken with successful results. This study is a preliminary investigation into this modified use of CDD and, it is hoped, will add to the ever-increasing body of knowledge concerning this material. These results may provide conservators with an alternative to the consolidation of pigments or inks on ceramics with acrylic resins or other materials that may be more permanent or difficult to completely remove, or which may alter the aesthetics of the object treated. This study has only begun to look into this particular use of cyclododecane, and, although further research is needed into the application of CDD to the desalination of inscribed archaeological objects, the results are promising.
Comparison of inscriptions (A) before treatment and (B) after coating with cyclododecane and desalination
The authors would like to thank Nancy Thomas, deputy director for curatorial affairs, and Victoria Blyth Hill, director of the Conservation Center at the Los Angeles County Museum of Art, for giving us the opportunity to conduct this research; Sara Caspi, conservator in private practice, for taking the time to discuss her CDD research; Brice Cantrell of the Department of Germanic Studies, University of Chicago, for his translation of the German articles; Alison Whyte, assistant conservator at the Oriental Institute Museum, for reading over and commenting on the early drafts; and Erik Risser, assistant conservator, Antiquities Conservation Department, J. Paul Getty Museum, for sharing his experiences with the use of CDD and for his editorial suggestions on the numerous versions of this article.
1. No details are given of the exact nature of the propellant or solvent in the aerosol spray can since it is proprietary information. The information available on the website (www.hangleiter.com) states that in the spray can, cyclododecane is present in a solved form with the propellant being the only solvent. The solvent is described as being extremely volatile.
APPENDIX 1. METHODS USED FOR THE EXAMINATION OF CDD'S WORKING PROPERTIES
1. Examination of Application Methods and Crystalline structure
Cyclododecane was applied in various forms on glass slides to compare the crystalline structures produced by different application methods. The application methods used were CDD as a melt, in solutions, and in an aerosol spray. A total of nine solvents were used to make up the solutions, for testing: petroleum ether, naphtha, isooctane, mineral spirits, dichloromethane, toluene, xylene, 1-1-1, trichloroethane, and heptane. These solvents were chosen based on their uses during similar published examinations, as well as by simply choosing previously untested solvents in which CDD was soluble. The degree of solubility of cyclododecane in each solvent varied, and therefore all solutions were made to the same concentration, 85% w/v, for consistency during testing. For the melt film, a heated spatula was used. A spraying distance of at least 3–4 cm was used for the aerosol spray, as recommended by Hangleiter (1999). The slides were examined using a binocular microscope, 10–40x magnification. Some of the films formed from the various application methods examined are shown in figure 2.
2. Determination of the Sublimation of CDD from Glass Slides and Terracotta Samples
Sublimation rate tests were conducted in a method similar to that used by Maish and Risser (2002) and Stein et al. (2000). Glass slides and several terracotta samples, measuring 3.5 x 4 cm and 7 mm thick, were coated for these tests. The surfaces of the samples were treated with cyclododecane as a melt, a spray, in petroleum ether, and in mineral spirits. Cyclododecane was applied until a 2 mm film was formed. The samples were kept uncovered and at room temperature (23°C, 40% RH) during testing. The sublimation process was monitored by weighing the samples before coating and then reweighing them every 24 hours until they reached their pretreatment weight. It was assumed that at this point, the cyclododecane would have sublimed completely from the sample.
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SOURCES OF MATERIALSColorhue Instant Set silk dyes
Things Japanese 9805 NE 116th St. Kirkland, Wash. 98034Cyclododecane
Kremer Pigments Inc. 228 Elizabeth St. New York, N.Y. 10012Cyclododecane—spray can
Hans-Michael Hangleiter GmbH Bismarckstrasse 13 D64853 Otzberg GermanyHiggins Fountain Pen India nonwaterproof black ink, item 46030 (723)
Sanford Bellwood, Ill. 60104Paper Mate nylon fiber point pen, Series 860, black ink, no. 863-11
The Gillette Co. Paper Mate Division Box 61 Boston, Mass. 02199Zephytronics AirPencil ZT-2
SMT Pin Point Soldering System 225 N. Palomares Pomona, Calif. 91767
VANESSA MUROS is an assistant conservator at the Oriental Institute Museum, University of Chicago. After receiving her B.A. in archaeology from Boston University, she completed the master's program in conservation at the Institute of Archaeology, University College, London. She has been an intern in the Metals Conservation Section at the British Museum and has worked as a conservator on various excavations. The research conducted for this article was completed during her Mellon Fellowship in Objects Conservation at the Los Angeles County Museum of Art in 2000. Address: Oriental Institute Museum, University of Chicago, 1155 E. 58th St., Chicago, Ill. 60637
JOHN HIRX is the head objects conservator at the Los Angeles County Museum of Art. For almost 10 years, he has worked in both conservation research and objects conservation, examining, analyzing, and treating works of art. In particular, he has focused on conservation and analytical studies related to ancient silver, Islamic ceramics, and seismic mitigation of LACMA's monumental sculptures. He has served as vice chair and chair for the Research and Technical Studies (RATS) specialty group of AIC. Prior to working at LACMA, Hirx worked for the Brooklyn Museum of Art, where he treated objects in the Egyptian collection prior to reinstallation, and for the Metropolitan Museum of Art. Address: Los Angeles County Museum of Art, 5905 Wilshire Blvd., Los Angeles, Calif. 90036