A study of the factors that affect thinning rates and damage processes during the ion-beam thinning of ceramics has been undertaken. The results of these studies are reported and related to the conditions necessary for the preparation of uniform damage free specimens. Particular emphasis is placed on the variations in specimen stoichiometry that can occur during ion-beam thinning. It is shown that under certain conditions the positively charged ion-beam can induce charged interstitial migration into the bulk of the sample. The extent to which this effect, atomic bonding, crystal orientation and beam conditions can produce non-uniform samples is discussed.