Copper for Archive Preservation
This article introduces a range of preservation products which the Society recently added to its stock for sale to members and the public. The products are based on a technology called Corrosion Intercept®. The development of the technology has an interesting history linked to one of the most publicised conservation projects of the last century: the centennial restoration, in the mid-1980s, of the Statue of Liberty.
At its first unveiling, in 1886, the Statue may have looked another penny-brown folly of human self-aggrandisement. In time, though, it came to acquire a poetic idea[1] that would transcend its original purpose[2]. And a beguiling crystalline green patina that would preserve that idea for posterity.
The Statue’s exterior is made of copper. From 80 tonnes of exceptionally pure, 6mm-thick copper sheet, hand-hammered down to about 2.4mm of exquisite detail in a process French craftsmen call repoussé. Most of the copper had been donated by the French copper magnate, Pierre-Eugène Secrétan.
Copper, like gold and silver, maintains the aloof atomic structure of a ‘noble’ metal. It doesn’t easily fall to ruin through liaisons with common corrupting elements like ‘base’ metals are prone to. Secrétan fell to ruin ̶ in the copper crash of 1889, three years following the Statue’s unveiling on Bedloe’s Island. His gift of copper, however, survived remarkably intact, losing about a tenth of a millimetre in a century of exposure to the harsh, corrosive New York Harbour environment. Less than 2% of the Statue’s copper sheath was found by conservators to require patching ̶ in areas where liquids had accumulated and caused abnormal corrosion, or which had sustained mechanical damage.
Reproducing the Statue’s green patina in the patched areas in time for the centennial unveiling presented a problem. A solution came from researchers confronted with quite the opposite problem – inhibiting the development of that patina in printed circuit boards (the cause of an intolerably high failure rate in telecommunications equipment).
The researchers, from AT&T’s Bell Laboratories[3], developed a method of ‘seeding’ patina crystals from the copper roof of their laboratory onto the newly patched areas of the Statue, and ‘growing’ the equivalent of a thirty-year patina in less than three months. The insights they gained from studying the Statue’s patina and developing the accelerated patination process aided their development of a product to protect printed circuit boards, and materials in general, from the corrosive effects of reactive atmospheric constituents.
The product, which they patented and named Corrosion Intercept®, is essentially a thin ‘reactive polymer’ barrier film made from copper that is chemically bonded to a polymer (typically polyethylene)[4]. It works by intercepting and neutralising reactive gases that permeate the film.
Reactive gases like nitrous oxides (NOx), ozone (O3), hydrogen sulphide (H2S), sulphur dioxide (SO2), carbonyl sulphide (COS) and hydrogen chloride (HCl), even in trace quantities, and particularly in the presence of moisture and ultraviolet light, are implicated in the degradation of most materials, including metals, plastics, rubbers, fabrics, paper, paints, ceramics, leather and magnetic media. Apart from acting as an effective barrier against reactive gases, Intercept films also have about half the moisture vapour permeability of clear polyethylene sheet of the same thickness. Additionally, the antibacterial, antiviral and anti-fungal properties of copper, well-recognised since antiquity, act to inhibit bio-deterioration due to these microorganisms.
While initially targeted at the electronics industry, conservators working in the museum sector immediately grasped the potential of Intercept® films for the preservation of archives, cultural artefacts and works of art. Intercept® films contain no volatile or abrasive additives and fillers, and pass the Photographic Activity Test and other archival criteria.
Intercept® products are currently being used by museums and galleries worldwide for wrapping and packaging objects for storage and transport; as backing for artwork (to intercept contaminants emanating from walls); for lining display and storage cases; for storage and preservation of fabrics, metallic threaded garments, coins and medals; and for long term storage of CDs and electronic media.
A feature of bags and enclosures made from Intercept® films is that they not only intercept reactive gases in the external environment, but also effectively scavenge and cleanse the internal microenvironments of reactive contaminants trapped or released (out-gassed) by the objects enclosed. The films also have an ‘in-built’ visual indication that signals it is working: When both sides of the film have turned a dark grey or white, the film has been effectively consumed and should be replaced. Intercept films may be expected to remain effective for more than ten years in typical indoor environments, and for three to seven years in more aggressive industrial or exposed situations.
A range of Intercept® products, including films, bags and foams, are on display and available for purchase at the Society’s shop in Nedlands. Or look up our online shop at https://shop.histwest.org.au/.
References and Further Reading:
Diamond, Stuart. ‘Technology; Statue’s Repair Aids Research’. The New York Times, 14 February 1985, sec. Business Day. https://www.nytimes.com/1985/02/14/business/technology-statue-s-repair-aids-research.html.
Franey, John P. Corrosion inhibition. United States US4944916A, filed 23 August 1989, and issued 31 July 1990. https://patents.google.com/patent/US4944916/en.
Franey, John P., and Dawn-Marie Sutton. ‘Static Intercept* Technology: A New Packaging Platform for Corrosion and ESD Protection’. Bell Labs Technical Journal 11, no. 3 (8 November 2006): 137–46. https://doi.org/10.1002/bltj.20184.
‘Innovations: Copper in My Medicine Chest?’ Accessed 15 September 2018. https://www.copper.org/publications/newsletters/innovations/2000/06/medicine-chest.html.
Keevil, Bill. ‘Copper Is Great at Killing Superbugs – so Why Don’t Hospitals Use It?’ The Conversation. Accessed 12 September 2018. http://theconversation.com/copper-is-great-at-killing-superbugs-so-why-dont-hospitals-use-it-73103.
Nagy, Eleonora. ‘Corrosion Intercept Tent Packing and Handling System for Donald Judd’s Brass and Copper Sculptures’. Objects Specialty Group Postprints, The American Institute for Conservation of Historic & Artistic Works 6 (1999): 11–35.
‘The Statue of Liberty’. Copper Development Association Inc. Accessed 3 September 2018. https://www.copper.org/education/liberty/.
[4] More accurately, a copper metal-oxide-semiconductor (MOS) covalently bonded to the polymer. In its usual form, the film is a lamination of three layers that are extruded and fused together without an adhesive: a polyethylene core layer, providing the strength and half the thickness of the sheet, sandwiched between two Intercept layers.↩