The etching of MgO smoke in wet conditions - an archetype for aqueous dissolution of oxide crystals is explored on the basis of transmission electron microscope (TEM) analyses. In pure water with neutral pH, in acid solutions and in moist air, the MgO cubic crystallites show first (110) truncations of the < 110 > edges and then (111) cuts at the corners. Criteria are given to characterize (110) and (111) cuts on the TEM images. It is shown that (110) truncations appear independently of the formation of the (111) cuts and are associated with a stationary state. The picture is fully consistent with the previous suggestion of a "constrained Wulff profile" [9] which explains the formation of (110) cuts by excluding (111) facets. (C) 2009 Elsevier B.V. All rights reserved.