New and artificially aged parchments were studied by unilateral NMR and micro DSC. Samples were obtained by exposing new parchments to 80 °C and alternate 40 and 80% relative humidity for increasing times up to 32 days. The impact of accelerated ageing was assessed by measuring both the proton transverse relaxation times (T 2eff ) and thermodynamic parameters associated with thermal denaturation of fibrillar collagen. Depending on the ageing time, significant structural changes correlated with thermal stability and collagen heterogeneity were observed, in good agreement with changes in phase composition and relaxation times. The results suggest two ageing regimes depending on the balance between the two main processes which drive the behavior of parchments during thermal ageing, i.e. thermally induced cross linking and thermal destabilization and denaturation.