Shaped gel articles that are formed within a mold cavity and that retain the size and shape of the mold cavity upon removal from the mold cavity, sintered articles prepared from the shaped gel articles, and methods of making the sintered articles are provided. The shaped gel articles are formed from a casting sol that contains colloidal silica particles that are treated with a surface modification composition that includes a silane surface modification agent having a radically polymerizable group. The sintered article has a shape identical to the mold cavity (except in regions where the mold cavity was overfilled) and to the shaped gel article but reduced in size proportional to the amount of isotropic shrinkage.