There is considerable evidence that sols, or colloidal oxides, can play a critical role as precursors to the primary particles of crystalline or amorphous oxides. Sols have been demonstrated to be useful precursors to form microengineered catalysts when adsorbed onto geometric structures, such as monolith honeycombs, or onto macroporous supports capable of allowing entry of the sol structure into the support interior. Sols tend to adsorb only on the exterior of conventional porous catalyst supports, presumably due to plugging of the pores at the exterior of the support particles. Such systems are microengineered structures in that the sol forms as a thin coating on the outer surface of the support particles forming a shell, or rim, configuration at the individual particle’s exterior. However, there is every reason for caution in the assumption that translated into the primary particles in the final oxide structure. Even the term sol-gel synthesis, prejudices the case that a sol is the precursor of the gel structure in a formal sense. Evidence presented in this paper makes a compelling case for some oxide systems that the sol structure, or sol size, is completely irrelevant to the primary particles which are present in the oxide that is formed during gelation. In these instances, the sol structure simply provides the nutrients which are transported to the growing crystals of the final structure. In contrast, for the case of aluminas formed from preformed sols there is apparently an upper threshold in size of the sol which serves to dictate the size of the primary particles of the crystalline alumina. Alumina sols below this threshold size lead to polymerization within the gel and formation of much more dense alumina structures. It is clear that the primary particles of aluminas are those crystalline particles which give rise to high surface area, and that these crystalline particles are intrinsic to the exceptional surface area stability of the, so-called, transitional aluminas. There are clear examples where the primary nucleation and growth processes, which are critical to the final oxide structure, are independent of the size of the sol precursor.