Laser cleaning of parchment: structural, thermal and biochemical studies into the effect of wavelength and fluence

Laser cleaning of parchment is a novel technique that has the potential to provide contactless, chemical-free cleaning of
historically important documents. However, the effect of laser cleaning on the collagenous structure of parchment is still poorly
understood, as is the effect of the wavelength or the energy density (fluence level) used to clean parchment. In this study, small
angle X-ray scattering (SAXS), shrinkage temperature (Ts) measurements by the micro hot table technique and SDSpolyacrylamide
gel electrophoresis (SDS-PAGE) of parchment samples after laser cleaning reveal the effect of cleaning to
the structural, thermal and molecular characteristics of parchment, respectively. The effect of cleaning at infrared (1064 nm),
green (532 nm) and ultraviolet (266 nm) wavelengths at a range of fluence levels is investigated. SAXS is used to investigate the
removal of dirt from parchment. Laser cleaning at IR or green wavelengths appears not to alter the collagen diffraction pattern
from SAXS, the shrinkage activity or shrinkage temperature from Ts measurements or the molecular integrity of parchment as
shown by SDS-PAGE. However, parchments cleaned at the ultraviolet wavelength display structural damage and a reduction in
hydrothermal stability and molecular integrity.