1. Rehydroxylation [RHX]: Some scientific comments and issues Christopher Hall University of Edinburgh School of Engineering Centre for Materials Science & Engineering UoE/National Museums Scotland Research Laboratory for Conservation Science

2. Moisture dynamics in buildings and masonry structures Hall, Hamilton, Viles et al 2010

3. Delta-Min Marie Curie Network Mechanisms of Mineral Replacement Reactions 2009-2012

5. Penn floor tile St Bride’s Church Fleet Street London UK Museum of London WFG62 Assigned date AD 1350-1390

6. Penn floor tile St Bride’s Church Fleet Street London UK Museum of London WFG62 Assigned date AD 1350-1390

18. Normalised stage 2 slope ln(α/α 25 ) plotted against 10 3 /T K -1, where α 25 is the interpolated slope at 25 °C, for three fired clay brick and tile samples. Red: Roman opus spicatum clay paving brick, London; blue: ‘Westminster’ clay tile, Merton Priory; green: clay brick, King Charles II Court, Greenwich Arrhenius plot: effect of temperature on rehydroxylation mass gain rate.

21. Samian ware: X-ray diffraction

24. Stackhouse, Coveney et al.

25. Stage I Stage II Variation of the fractional mass gain (Δm/m o ) with the fourth root of time (time) 1/4 of kaolin samples fired at different temperatures [Hesham Mesbah]

26. Open questions Why (time) 1/4 ?

28. A Putnis Rev Mineralogy Geochem 2009 Pseudomorphic replacement of calcite and aragonite by Hydroxyapatite Normal diffusion (time) 1/2

30. Lizana and Ambjörnsson Phys Rev Lett 2008 v100 20601

32. Open questions Why (time) 1/4 ? … and, if single-file diffusion, on what structure?

34. Open questions Why (time) 1/4 ? … and, if single-file diffusion, on what structure? Why rehydroxylation when firing has proceeded to 1050 °C? Does accurately describe the entire process on 1000 year time scales?

35. Some conclusions Incontrovertible evidence that the RHX process occurs more or less universally in all fired clay ceramics Strong evidence that the (time) 1/4 clock is valid Data acquisition for a single sample is still laborious Major validation studies needed Mechanistic and materials fundamentals not fully understood

36. Acknowledgements Moira Wilson, Margaret Carter, Ceren Ince, Bill Hoff, Hesham Mesbah (Manchester) Andrea Hamilton (Edinburgh)