THE COMPOSITIONS OF ICE SHELLS PROVIDE CLUES TO THE BULK COMPOSITION OF ICY WORLDS AND THEIR CURRENT OR PAST LIQUID RESERVOIRS. THEY ARE ALSO KEY INFORMATION TO UNDERSTAND PROPERTIES AND PROCESSES WITHIN THE ICE SHELL WHICH DETERMINE THE NATURE AND TIMESCALE OF TRANSPORT OF MATERIAL BETWEEN LIQUID RESERVOIRS AND THE SURFACE. THIS INCLUDES THE DELIVERY OF SURFACE OXIDANTS GENERATED BY RADIATIVE PROCESSING OF SURFACE H2O ICE TO THE OCEAN WHICH COULD MAINTAIN A REDOX DISEQUILIBRIUM THAT LIFE COULD TAP AS AN ENERGY SOURCE AND THE TRANSPORT OF OCEAN MATERIAL (INCLUDING POSSIBLE BIO SIGNATURES) TO THE SURFACE WHERE IT CAN BE DETECTED BY SPACECRAFT. ALTHOUGH ICE SHELL COMPOSITIONS ARE KEY TO THESE PROCESSES THE CHEMISTRY OF ICE SHELLS REMAINS POORLY UNDERSTOOD AND UNDERSTUDIED. ONLY A FEW GEOCHEMICAL STUDIES HAVE SOUGHT TO CONSTRAIN BULK ICE SHELL COMPOSITIONS BASED ON FREEZING SEQUENCES. IMPROVEMENTS IN GEOCHEMICAL MODELS OF FREEZING SOLUTIONS AND NEW DATA ON THE COMPOSITIONAL DIVERSITY OF ICE CRUSTS IN THE PAST FEW YEARS WARRANT REVISITING THESE CALCULATIONS AND APPLYING THEM TO THE UNDERSTANDING OF ICE SHELLS IN GENERAL AND THOSE FOR WHICH SURFACE COMPOSITIONS HAVE BEEN MEASURED IN PARTICULAR.