Sea ice beams were cut using a technique already developed to stress sea ice to fracture. Twenty two beams were cut in total. Mechanical measurements and characterisation of the resulting cracks was completed both before and after refreezing by using brine volume, thermal and optical measurements. The processes of stressing the ice to the point of fracture was monitored using acoustic emission ... measurements. The data obtained from the sea ice beams was used to characterise a range of naturally occurring cracks and imperfections and to relate these to the physical performance of the ice sheet as a whole. Slots that were cut in the sea ice during refreezing were excavated at specific time intervals to observe the progress of freezing by recording the interface shape, and the ice thickness in the crack. The sea ice crystal structure in the cracks, and salinity profiles through the cracks were recorded. In addition, the time evolution of the temperatures and the final distribution of salinity and the crystal structure during the refreezing of a parallel sided crack was measured. The flexural strengths of refrozen cracks of constant width were investigated as a function of time of refreezing. Measurements of the diffusive spreading of light across these deliberately prepared re-frozen cuts in the ice were also conducted.