Maarten van Bommel Lorraine Gibson Simon Watts Velichka Kontozova Lieve Halsberghe

1. A comparison of diffusion tube determinations of formic and acetic acid concentrations in air Maarten van Bommel Lorraine Gibson Simon Watts Velichka Kontozova Lieve Halsberghe Brought to you by Agnes Brokerhof

2. Introduction Efflorescence observed on ceramics in showcases in Kortrijk, Belgium Nishapur showcase

3. Analysis • Analysis of the salt indicates mainly acetates • Analysis of concentrations acetic and formic acid in the air was not consistent • University of Antwerp • Strathclyde University • Netherlands Institute for Cultural Heritage (ICN) • Pilot project: comparison study • Oxford Brookes university joined

4. Palmes tubes Diffusion from open end to sorbent Radiello tubes Diffusion through permeable wall Pilot project • Deploy tubes to an environment with known concentration formic and acetic acid • Deploy tubes in different showcases at the same time • Two type tubes used:

5. Preparation of calibration gas Water out Air out, followed by dilution with air Air in, 100 ml/min Permeation tube Water in, 50 °C

6. Deployment in exposure chamber T = 23.0 °C, ± 0.1 RH = 50.0% ± 0.5 Computer fan applied

7. Deployment in showcases Bible tile showcase tubes randomly deployed Nishapur showcase tubes grouped

8. 700 600 Concentration (ppb) 500 400 300 200 100 0 Strathclyde Antwerp ICN Oxford Results exposure chamber Calc HFor Calc HAc Formic acid Acetic acid

9. 700 600 500 400 300 200 100 0 Strathclyde Antwerp ICN Oxford Results exposure chamber Calc HFor Not an official interlaboratory comparison! Calc HAc • Individual operators are consistent • HFor: close to calculated conc • Accuracy factor 2 • Precision 4-40% • HAc: more spread from calculated conc • Accuracy factor 2 • Precision 2-20%

10. Nishapur Porcelain Biblical tiles Outside Results showcases, acetic acid 800 700 Concentration (ppb) 600 500 average 400 average 300 200 100 0 Strathclyde Antwerp ICN Oxford

11. Nishapur Porcelain Biblical tiles Outside Results showcases, formic acid 600 500 Concentration (ppb) 400 300 average 200 average 100 0 Strathclyde Antwerp ICN Oxford

12. Nishapur Porcelain Biblical tiles Outside Preservation target, acetic acid 800 700 Concentration (ppb) 600 500 1 yr 400 300 200 100 10 yrs 0 Strathclyde Antwerp ICN Oxford

13. Discussion & Conclusions Exposure chamber • Not bad considering no SOPs • All operators consistent • ICN is closest to values in exposure chamber • Transport effect or delay of analysis • HAc known to degrade, analyse as soon as possible • Antwerp consistently lower • Strathclyde HAc consistently higher – attention • Use several exposure chambers for comparison • Keep factor 2 in mind

14. Discussion & Conclusions Showcases • Values HAc vary factor 2 from average • Strathclyde high • Oxford low • Consistent with exposure chamber • Values HFor vary factor 2 from average • Oxford high • Antwerp low • Consistent with exposure chamber • Relative values important – in/out • Consequences for mitigation • Interpretation requires knowledge

15. Best regards from the authors