Many studies, based mostly on ultra-sensitive length measurements, have revealed dimensional micro-instabilities in various optical materials. In some components, probe arrays and interferometric methods have also revealed changes in surface figure over time. Both types of measurements have shown that creep can be observed over periods of days, to months, and years. The typical asymptotic form of the aging curve points to the relaxation of structural or embedded stress. However, details of the mechanisms involved are not well understood. Additionally, the results of an interferometric study of an optical flat over a period of several years have provided some specific indicators for further studies in this area. For example, the extremely small change in shape of the surface was found to be rotationally symmetric, and hence apparently unrelated to the large amount of internal strain non-uniformly distributed throughout the flat substrate. This change in shape approached a limiting value after a period of eight years. The form of this curve suggests that the activation of the change was initiated at the time of the component fabrication, and not at the time of material manufacture. Some scenarios for possible sources of the observed change are discussed and some critical tests are suggested with the aim of clarifying the role of possible mechanisms responsible for long-term changes. Finally, a practical method for using an oil film as a reference standard of flatness in a Fizeau-type interferometer is presented.