Adhesives and their Application

Hosted by the National Records of Scotland at the General Register House in Edinburgh on 5 November 2014, and organised by the Archives and Records Association Preservation and Conservation Group (ARA), this training day on adhesives and their applications followed on from one held at the Norfolk Record Office one year prior. A keenly interested audience of conservators from across the UK attended the course, which included talks presenting research on the ageing properties and practical applications of adhesives in the conservation of archival and non-archival materials, with a focus on leather and parchment.

Ageing Properties of Adhesives

Mary French opened the morning session, discussing some outcomes of work from her MA research, ‘Investigating the Ageing Properties of Lascaux 303 HV and 498 HV on Paper and Leather’.

Lascaux 303 HV, which replaced 360 HV when it was discontinued in 2012, and 498 HV are acrylic adhesives whose properties make them particularly suitable for the conservation of a large range of materials. 303 HV features permanent tack, a high degree of flexibility at room temperature and transparency on drying. Both are water soluble before drying and, according to the manufacturer, permanently soluble in acetone, alcohol, toluene and xylene.

Mary carried out a usage survey that showed that Lascaux adhesives were most used by respondents on the following: 75% used Lascaux on leather; 50% of respondents used it on paper, while 37.5% used it on parchment.

The most popular uses were: 75% for making heat-set tissue, 62.5% for consolidation of degraded leather and 50% for making solvent-set tissue.

An experiment was set up to examine the long-term ageing effects of Lascaux 303 HV, 498 HV, and EVACON-R on paper and leather and their suitability for conservation treatments. This comprised the preparation of samples of Lascaux 303 HV, 498 HV and EVACON-R. These adhesives were tested on K145 Japanese paper, Bodleian handmade paper, archival vegetable-tanned calfskin and each was also tested as a stand-alone film.

These samples were kept in an ageing chamber at 70⁰C for a period of 5 weeks, which was estimated to represent approximately 3.5 years.

The samples were assessed for changes in colour, chemical structure, pH, solubility, reversibility, shrinkage temperature and off-gassing of volatile acidic components, with the following results:

• The colour change in adhesive samples was tested using a Konica Minolta Spectrophotometer. The change in colour of the leather samples was significantly greater than for the other materials, with most to least changed as follows: uncoated, 303 HV, 498 HV, EVACON-R. The other materials showed no significant change.
• FTIR analysis indicated that the chemical structure of the samples had remained virtually unchanged.
• All adhesives increased the initial pH value of 5.27 of the water that they were dissolved in, the pH decreasing with ageing but remaining above that initial value. EVACON-R was the exception, with the pH of the water continuing to increase after ageing.
• Solubility tests were carried out using acetone, propan-2-ol, and xylene. All samples remained soluble, with EVACON-R being the least soluble. Reversibility tests produced diverse results, although all adhesives proved difficult to remove from porous or fibrous materials.
• There were no significant changes in the shrinkage temperature of the leather.

Two different tests for off-gassing were carried out:

• A-D strips, which only reacted with EVACON-R
• Oddy Testing: EVACON-R released acetic acid, and Lascaux 498 HV released sulphur compounds

Mary advanced several ideas for furthering her research on these products: a different ageing regime that factors in relative humidity, off-gassing from Lascaux 498 HV and EVACON-R; the use of Lascaux on parchment; bond strength and reversibility of heat- and solvent-set repair tissues.

A brief summary and bibliography of previous research on the ageing properties of these products can be found in the June 2014 newsletter of the ICOM-CC Leather & Related Materials working group.

Adhesives for Parchment Repair

Dominic Wall, from the Suffolk, UK Record Office, has worked extensively on the conservation of damaged parchment. His talk presented an overview of the evolution of his approach and treatment methods in two directions: the repair of badly damaged parchment and the consolidation of damaged parchment surfaces.

This evolution has largely been informed by the need to minimise the amount of moisture introduced during treatment of parchment, taking into account three main factors: the frequent presence of iron gall ink, the hygroscopic nature of parchment and the need for greater control over the physical intervention on the objects.

Dominic described two repair methods:

1. Goldbeater’s skin, pre-coated with gelatine and faced with spider tissue adhered with Klucel G to facilitate handling. Cold gelatine is used to reactivate the adhesive and the facing tissue is removed with acetone after application. This technique has a short drying time. Paper Nao K32 was used for infilling. Dominic has also used goldbeater’s skin combined with Japanese paper

2. Acrylic-coated (by spraying or pasting through) 5 gsm Japanese paper laid on silicone-coated paper, using either:

• Plextol B500/M630 (2:1 in 9 parts of water). Reactivated with IMS. One of Dominic’s aims is to use as little adhesive as possible, hence the relatively low concentration

• Lascaux 498 HV in water (1:5). Reactivated with acetone. Lascaux adhesives require a higher concentration to produce the desired strength

The second method has a shorter drying time.

For the consolidation of parchment surfaces, Dominic considers two types of damage, depending on whether the unstable element is the medium or a delaminating parchment substrate. The former includes both the degrading chemical reaction catalysed by metallic inks and the cohesive and adhesive failure of the ink binder.

Dominic tackles both cases by locally misting a 1% isinglass solution aided by gently tapping down on the area with a cotton swab. The treatment is carried out on a vacuum table. The treated surface of the document is covered with Gore-Tex. In order to increase control over the amount of moisture applied to the membrane, Dominic has successively tried several devices aimed at reducing the size of the droplets in the mist flow: the ZFB AGS2000 ultrasonic humidifier (Ø 5 μm droplets), the Portaneb nebulizer with Sidestream attachment (Ø 1-2 μm droplets) and the Partulizer solvent-proof, aerosol generator (Ø <5 μm droplets) developed by Dr Andrea Pataki-Hundt.

Adhesives for Leather

Yvette Fletcher, Head of Conservation at the Leather Conservation Centre (LCC), delivered a talk on adhesives for leather conservation.

Within the LCC’s daily practice, adhesives are applied to materials such as Japanese papers, dyed non-woven polyester (e.g. Reemay) and in-house dyed conservation-grade leather. In order to test the ageing properties of the adhesives applied to leather, the LCC has an accelerated ageing chamber set up to produce an equivalent of 100 years of ageing in 12 weeks. Occasionally, the LCC also benefits from the tannery facilities in the neighbouring Institute of Creative Leather Technologies of the University of Northampton.

Yvette stressed the need to consider several factors before choosing an adhesive, including: pH, molecular weight, particle size, glass transition temperature, viscosity, moisture content, drying time, shrinkage, strength of bond, flexibility, surface finish, visual appearance, reversibility, ageing properties, discolouration, sacrificial repair, health and safety and cost – as directly related to shelf life and availability (click here for a PDF summary).

The delegates had the opportunity to examine several samples of a single type of leather combined with different adhesives, including: wheat starch paste (not recommended for leather-to-leather joints), wheat starch paste mixed with reversible PVA, Beva film, Lascaux 360 HV and 498 HV and Vinamul. According to Yvette, adhesives such as hide glue or contact adhesive should be discarded, even if the latter can be dissolved in toluene. Acetone should be avoided in the treatment of leather. (correction, 24.06.2015: the article as first published incorrectly stated that the use of white spirit was discouraged for the treatment of leather)

Adhesives for Remoistenable Tissue

The fourth and final presentation of the day described the very interesting research and practice developed by Antoinette Curtis and Yuki Uchida-Russell at the Norfolk Record Office (NRO): A protein journey: adhesive choices for coating remoistenable tissue.

Antoinette and Yuki had previously presented the poster Which gelatine to use? The choices for conservators at the Adhesives and Consolidants for Conservation symposium at the Canadian Conservation Institute in Ottawa in 2011.

The NRO conservators’ preference for gelatine and isinglass for parchment treatment is based on:

• The principle of ‘like for like’, in this case the compatibility between materials of similar proteinaceous nature
• Stability over time as demonstrated by historical evidence and specialist research
• Control over the mobility of the adhesive
• The adhesives’ commercial availability

Antoinette started off her talk by reminding us of the key properties of gelatine for conservators: bloom and type, and their influence on pH, viscosity and strength.

At the NRO, gelatine is used for:

• Consolidation: 1% type A, relatively low bloom (i.e. 100), as a warm solution
• Tear repair and infills: 3-5% type A, medium-high bloom (i.e. 200), in mousse state
• Poulticing, for which a higher concentration (8-10%) is required to avoid an excessive moisture release: Dr Oetker Select leaf gelatine (type A, 230 bloom) is locally applied as a rigid gel, sandwiched between pieces of spider tissue, placed underneath, in contact with the object and polyester film, under light weight

The conservation of the Manor of Aylsham Lancaster court roll, 1509–46 (NRS 13434), supported by the National Manuscripts Conservation Trust and Aylsham’s local community and undertaken between September 2012 and March 2014, was a challenging opportunity for testing new combinations of existing materials and techniques, among them isinglass, Gossamer or Berlin Tissue and Zorbix.

In its purest form, isinglass is made from the membrane of the sturgeon air/swim bladder. Compared to gelatine, isinglass presents a neutral pH and no bloom value. Some of its advantages are slow gelling time, flexibility and fast hydration for application and removal. Disadvantages include an undesirable sheen with light repair material and sensitivity to RH fluctuations. New international regulations restricted the fishing of wild sturgeon in 1998, and the most commonly available isinglass nowadays is a by-product of German sturgeon farming in caviar production.

Gossamer, or Berlin Tissue, is a 2 gsm matt paper made of kozo (30%) and mitsumata (70%) fibres, developed by Franklin Mowery and produced by Gangolf Ulbricht in Berlin. Mitsumata fibres help to reduce the sheen produced by, for example, gelatinous adhesives. At the NRO, a 1.5% isinglass solution is applied with a sizing hake (brush) by brushing through the tissue laid on a thick Melinex sheet lined with a matt, textured film.

The most innovative aspect of the process is the use of Zorbix to reactivate the adhesive in the tissue. In 2011, Nicholas Yeager (Artifex Equipment Inc.) announced the commercial launch of Zorbix as “a reusable, super-absorbent sheet for quickly drying water-damaged books and documents”, claiming that it could absorb “50 times its weight in water, making it 25 times as effective as blotter paper”. However, other than for drying purposes, Zorbix soon showed itself ideal for controlled humidification, due to the gentle moisture release from its inner starch reservoir.

The repair process is as follows:

• The document, supported by a sheet of Bondina, is laid on a low-pressure suction table with a shaped piece of pre-coated tissue placed over the area requiring repair
• Polyester film discs are used to mask the areas of the document not requiring hydration
• A sheet of hydrated Zorbix is laid on top
• This is covered with a sheet of polyester and the vacuum is turned on for 3–5 minutes
• The object is put to dry between Bondina and wool felts under weight overnight. The opposite side is repaired the following day, after which the document is left to consolidate under weight for up to six months.

Antoinette provided a hard copy version of the 2011 symposium poster and other useful handouts.

The high interest of the training day’s subject and the different approaches presented by the speakers prompted a lively discussion session, followed by the chance to look at the materials displayed by Antoinette Curtis to close the day.

The event took place in the Media Room of General Register House, Edinburgh, the oldest European purpose-built archive that still keeps its original use. The space was just right for the audience and for the display of materials brought by the speakers. The technical equipment included a nicely sized screen for presentations. The refreshments provided were also much appreciated!

Salvador Alcántara Peláez is a graduate in History of Art, and has an MA in Museum Studies. He completed an FdA in Book Conservation at Camberwell College of Arts, London, which was followed by an HLF internship at the Wellcome Library. He is now conservator at the National Records of Scotland, Edinburgh.