3.2. Glass powdersGlass powders are routinely prepared by milling frits. Other methods of preparation(e.g., melt spraying) and exotic sources of glass (eg, glass fragments from shock wave treatments of crystalsare conceivable, including a direct production of glass powders by a che-mical route such as flame/plasma pyrolysis. If glass powders are used to shape a green body (plus additives/binders which are burned-out during firing), the subsequent heat treatment allows not only for nu-cleation and crystal growth at surfaces and in the volume of glass particles, but also for viscous sintering The latter allows low-cost ceramic shaping technologies, but it causes considerable shrinkage and the resulting products often contain some residual porosity. It then follows that two of the most outstanding benefits of glass-ceramic processing, ie., neat net-shaping and the absence of porosity, are lost.To display these striking differences, glass-ceramics- produced by the powder route are named sintered glass-ceramics [38] or frit-derived glass-ceramics [8]. The same applies to layers and films of glass powders sintered on, or fused between, any substrates if controlled crystal-lization is used to reach desired properties. However, these materials are assigned to glass-ceramics since the chronological sequence of the three core processing steps, i.e. (i) glass formation, (i) shaping an ar-ticle, and (ii) ceramming the article, remain preserved. Differences apply only to the type of shaping, which is in the traditional glass-ceramic route a hot-forming process above T, whereas, using powders,articles are shaped by cold-forming(casting, spraying, dipping, etc.)at ambient temperatures (T