Old Treatment, New Problem: Bakelite as a Consolidant

Figure 1. First stage in the polymerisation of phenol formaldehyde (C.V. Horie, Materials for Conservation, Butterworths 1987, pg. 176) (click image for larger version)

Bakelite is a trade name of the phenol-formaldehyde resin, which is one of the earliest synthetic polymers. It was manufactured in the first decade of the 20th century and found various applications. In the 1920s, it began to be applied as a coating for conservation purposes, on fossils and wooden objects that required consolidation.

Although it was suggested in contemporary publications as an excellent coating resin, its recorded use was restricted to fossil bones in the Chicago Field Museum, in the USA and in the Natural History Museum in London, UK. Bakelite applications in conservation were discontinued in the 1940s because of certain disadvantages that soon became apparent. The lack of records and relevant information precludes any assumption on the extent of its use and in which institutions.

Its discovery is attributed to the German chemist A. Von Bayer who produced the resinous substance out of acid, formaldehyde and phenol in 1878¹. However, Bakelite was not manufactured until 1909, when Leo Hendrick Baekeland established the Bakelite Company in the United States with branches in Europe. Bakelite was also produced from 1915 by the London-based Damard Lacquer Company and in 1926 the two companies merged to form Bakelite Limited² .

The resin offered many advantages that current raw materials could not always provide. For instance, the rapidly-evolving technological evolution of those times required strong and durable materials for specific applications, like the insulation of electrical cables, and Bakelite was offered as the solution as opposed to the current natural or semi-synthetic substances. Furthermore, its properties allowed it to be moulded in order to produce long-lasting objects at low cost, from ornaments and handles to radiophones and furniture, rendering Bakelite a radical medium³ .

The formaldehyde family of resins are highly cross-linked polymers formed by condensation reactions. The process of polymerisation takes place in two stages. First, water-soluble oligomers of formaldehyde and phenol are created by a condensation reaction (figure 1). The oligomers that result can be directly used for casting or as a varnish. At the second stage the oligomers are cross-linked by acid catalysts or heat, forming the longer polymer and a large amount of water is produced. The polymers can also be used as a varnish if applied as a coating, thin enough for water produced in the reaction to be released⁴ . Bakelite varnish is a brittle material, described as a completely irreversible thermosetting resin. It is yellow to dark brown, unevenly transparent, light-sensitive and it darkens over time.

Figure 2. Angle capital, English, limestone, 13th century (V&A A76-1916). Photograph by Metaxia Ventikou (click image for larger version)

The first reference to the use of Bakelite as a consolidant dates from 1925 when it is suggested for the hardening of fragile fossil bones⁵. The process is briefly described thus: Bakelite Varnish was thinned with Bakelite Thinner, a flammable and volatile substance, supplied by Bakelite Ltd, about which no further information is given. This was brushed onto the bones or they were immersed in it. Residues were washed away with the thinner or with a mixture of alcohol and amyl acetate. After draining for several hours, the bones were baked in an oven for about 15 hours at 220^o F. The solvent evaporated and the Bakelite was polymerised to a 'hard, durable and practically indestructible substance'⁶. Apparently, the Bakelite Varnish consisted of phenol-formaldehyde oligomers, which were polymerised upon exposure to high temperatures. 

After 1930, the Field Museum of Natural History in Chicago and the Natural History Museum in London adopted the technique with only slight variations. Bakelite replaced the natural and semi-synthetic resins previously used. Compared to natural resins such as paraffin wax, glue, gum arabic, mastics and Shellac, Bakelite was believed to have better properties such as its indestructibility after curing. It was reported to penetrate bone four times more deeply than Shellac, it was more elastic and left the treated specimens hard and tough⁷. By the early 1940s, Bakelite's disadvantages were apparent; it was a brittle, irreversible material, which darkened the objects. New resins, such as vinyl acetate, became more suitable for consolidation purposes since they could be easily removed by a solvent and did not alter the appearance of the objects⁸. 

The use of Bakelite as a consolidant seems to have been restricted to fossil bones and, to a lesser extent, to wooden objects, from the 1920s to the 1940s. Although it is possible that Bakelite may have been tested, or even applied, on other types of objects, no records have been found. Its identification on an architectural fragment in the V&A collection was unexpected and sheds some light on its use as a consolidant.

Figure 3. FTIR spectra of a. Bakelite standard, b. Bakelite coating on A88-1916 and c. Bakelite coating on A76-1916 (click image for larger version)

The 13th century limestone angle capital (A76-1916) was covered with an unidentified, uniform, dark brown layer that did not resemble any of the deterioration layers commonly found on stone objects, or to any known coatings (Figure 2). Its presence on some areas of loss confirmed that it was not an original layer but was applied much later, apparently for preservation purposes since the stone is heavily deteriorated. However, the dark brown layer proved inadequate for securing the loose pieces in place. Attempts to dissolve the layer with various solvents, such as white spirit, ethanol, acetone, iso-propanol, toluene, xylene and mixture of ammonia and water, completely failed.

A sample was taken for identification by Fourier Transform Infra Red (FTIR)spectroscopy in the Science Group of the V&A. The spectrum corresponded to the Bakelite reference spectrum (Figure 3). The dark brown coating was, beyond doubt, Bakelite. This raised more questions regarding the application date and the usage of Bakelite Varnish in the V&A. Was the capital an isolated case, perhaps an experiment, or was Bakelite treatment common in the Museum? 

The capital was acquired in 1916 and belongs to a large group of architectural details donated in the same year by the Architectural Association. Although Bakelite was being produced since 1909, its application as a varnish before 1916 does not seem probable. A 1919 V&A publication of Recent Acquisitions describes the donation of the collection in 1916 and mentions that 'some considerable time had been spent in cleaning the objects and 'treating them for decay'⁹. 

 Recent examination of the collection revealed that the most fragile pieces were covered by a similar dark brown layer that could be presumed to be Bakelite; objects of marble or other polishable stones had not undergone consolidation treatment. A coating from a 13th century architectural moulding (A88-1916) (Figure 4) was analysed by FTIR spectroscopy. The spectrum exactly corresponded with both the Bakelite reference and the angle capital spectra (Fig. 3 spectrum B). Although more coating samples must be analysed, it can be supposed with certainty that Bakelite was used for the consolidation of objects from this collection.

Figure 4. Architecture moulding with tooth ornament, English, limestone, 13th century (V&A A88-1916) Photograph by Metaxia Ventikou (click image for larger version)

If the 'treatment for decay' mentioned in the 1919 record refers to consolidation with Bakelite, this predates the earliest recorded such usage by at least six years. However, the V&A collection could have been treated with Bakelite at a later date, perhaps during the 1930s when this was common practice. A second programme of treatment within a relatively short time seems unlikely to have been carried out, but even if this is the case, the V&A architectural collection is still significant as a new example of stone consolidation with phenol formaldehyde resin.

The detection of Bakelite on stone objects reveals a previously unknown application of this resin. For over two decades Bakelite was regarded as an excellent conservation material and its identification on stone objects in the Victoria and Albert Museum shows that it could have been used as a consolidant in other types of objects as well. Conservators frequently come across old conservation materials and Bakelite must be considered as such from now on. Further study is necessary to determine the extent and implications of Bakelite's past use. It is hoped that this brief overview will serve as a useful introduction to the use of Bakelite as a stone consolidant.

Acknowledgements

I would like to thank Ms Charlotte Hubbard for all the guidance and the translation of the German article, Mr William Lindsay for the useful information, Dr Brenda Keneghan and Ms Silvia Valussi for the identification of Bakelite, Dr Paul Williamson and Ms Peta Motture for allowing me access to the Architectural Collection, and Mr Pedro Gaspar for his comments.

References

1. Müller-Straten, C.,  Die Anfänge des Kunststoffs: 1839-1925 , Restauro 1, 1988, pp30-37.
2. Reboul, P., Britain and the Bakelite Revolution in Mossman, S. T. I., and Morris, P. J. T., (eds.) The Development of Plastics, The Science Museum, London, pp26-37.
3. Meikle, J. L., Materia Nova: Plastics and Design in the U.S., 1925-1935 in Mossman, S. T. I., and Morris, P. J. T., (eds.) The Development of Plastics, The Science Museum, London, pp38-53.
4. Horie, C. V., Materials for Conservation, Butterworths, London, 1987, pp175-177.
5. Case, E. C., The Use of Bakelite in the Preservation of Fossil Material, Science 61, n. 1586, 1925, pp543-544 and Nichols, H. W. and Orr, P. C., Bakelite Impregnation of Fossil Bones, The Museum Journal 32, 1932, pp47-53.
6. Nichols, H. W. and Orr, P. C. op.cit.
7. Case, E. C. op.cit. and Nichols, H. W. and Orr, P. C. op.cit.
8. Howie, F. M. P., Conserving and Mounting Fossils: A Historical Review, Curator 29, 1986, pp5-24.
9. Victoria and Albert Museum, Review of the Principal Acquisitions During the Year 1916, London, 1919, pp. 1-2.