LONGITUDINAL velocity gradients in a flowing system have a powerful orienting influence on macromolecules and have been used to align polyethylene chains immediately before crystallisation1 and from the melt2. Corning 119 SCR is a glass which crystallises to a glass ceramic containing fluorophlogopite (mica) as the principal crystalline phase. By subjecting it to pure extensional flow during crystallisation, strict alignment of the fluorophlogopite crystals has been achieved. Once produced, the alignment is maintained during subsequent drawing down to fibre diameters of less than 100 µm.