Kath Eremin

The National Museums of Scotland

Materials testing for the Museum of Scotland: Did it prevent pollutants?

Summary

Materials testing was undertaken for materials to be used in showcases and galleries in the Museum of Scotland in order to eliminate internal pollutants. Pollutant levels were monitored in the museum during construction and in the first year of opening to check whether this had been achieved. Initially, levels of formaldehyde were high in cases and galleries due to ongoing construction work but fell subsequently. In contrast, levels of acetaldehyde remained high in cases and are attributed to off-gassing of liquid finishes. Measurement of levels of organic acids are planned as it is possible that the acetaldehyde may oxidise to acetic acid. No corrosion has been observed on any artefacts or on metal tokens placed in the cases.

Introduction

Materials testing was undertaken for a large number of products (including fabrics, paints, varnishes, adhesives and sealants) to ascertain their suitability for use in the new Museum of Scotland, which opened on November 30^th 1998. The main tests used were the Oddy and pH tests. As fibreboard was required in the cases, emissions of organic gases from samples of board were measured and the different boards compared (Eremin & Wilthew, 1996, ICOM preprints). The lowest emissions were obtained from zero-formaldehyde medium density fibreboard but emissions of organic acids remained high and some aldehydes were also emitted. A variety of products that claim to reduce or eliminate such emissions were applied to samples of ZF MDF and the emissions of organic gases measured. This indicated that only the barrier foils eliminated all organic gases, whilst all liquid sealants allowed emission of some gases, particularly the organic acids. Since a paint finish was required and it is not possible to paint over the barrier foils, the cases were assessed by object sensitivity to organic gases.

Three different schemes were proposed: cases with very sensitive artefacts should have ZF MDF with a barrier foil and approved textile, cases with artefacts with moderate sensitivity could have ZF MDF with the best liquid sealant (Nextel) and cases with artefacts of low sensitivity could have ZF MDF with any approved finish. This was, however, not used as finalised object lists for cases were not available and it was decided that all cases should have the same finish. As a result, ZF MDF with Nextel was used in all cases and concerns about organic pollutants remained. Other sources of internal pollutants are thought to have been eliminated, eg. no carpets are used in MOS, and the case carcasses are constructed of inert, approved materials.

Results

Two showcases were supplied for testing and levels of organic acids and aldehydes were measured in these. Initially formaldehyde levels were extremely high with values of 651 ppb to 716 ppb in cases compared to 81 ppb in the gallery area, although these were reduced after 3 weeks to 114 ppb to 521 ppb in cases with 33 ppb in the gallery. Acetaldehyde levels were much lower, with initial values of 11 ppb to 45 ppb in cases and 39 ppb in the gallery and final values of 22 ppb to 46 ppb in cases and 4 ppb in the gallery. The higher initial levels and high gallery levels were attributed to off-gassing of the ZF MDF and the paint finishes in the area and cases. The organic acids were only measured once and case levels ranged from 78 to 115 ppb for formic acid and from 130 to 209 ppb for acetic acid, with gallery levels of 62 ppb and 58 ppb respectively. The appreciable final levels of organic gases were attributed to poor application of the sealant to the ZF MDF, which was observed visibly, and it was hoped that the levels would be significantly lower in the final cases.

The levels of organic gases in cases in the Museum of Scotland were monitored on several occasions during and after installation as it was observed that the cases had a strong chemical odour. Levels of formaldehyde in October '98 ranged from 72 ppb to 443 ppb in galleries and from 110 ppb to 530 ppb in cases, with some galleries having higher levels than the associated cases. These high levels were attributed to on-going building work and cutting of wood products, including fibreboard, in gallery areas. Higher molecular weight aldehydes were detected in cases but not in galleries. Levels were re-measured in July '99: levels of formaldehyde ranged from 25 ppb to 128 ppb in cases and from 18 ppb to 33 ppb in galleries, with case levels always higher than gallery levels. Levels of acetaldehyde in July '99 ranged from 24 ppb to 209 ppb in cases and from 2 to 25 ppb in galleries, again with case levels always higher than gallery levels. The levels of acetaldehyde are surprisingly high and are attributed to continued off-gassing of a product in the cases, probably the Nextel. Although it has not been possible to undertake a detailed conservation inspection there are no visible signs on any artefacts or on the lead tokens that were placed in the cases (although these have now been removed). Although no references to corrosion from exposure to acetaldehyde have been found, there is the possibility that acetaldehyde could be oxidised to acetic acid, hence that levels of organic acids may be a concern. Levels of organic acids were measured in July '98 and levels of 321 ppb of acetic acid were detected in one case with 210 ppb in the gallery. Levels are to be re-measured in September '99.

Conclusions

Although materials testing did not succeed in eliminating all internal pollutants from MOS, current levels are fairly low and no corrosion has been observed to date. The possibility of oxidation of acetaldehyde to acetic acid remains a concern and levels of organic acids will be measured.