Abstract: A method for producing a large quartz-glass pipe is provided. In a first forming step, an intermediate cylinder made of quartz glass and having an intermediate-cylinder wall thickness and outside diameter is formed by using a forming tool and is then cooled. In a second shaping step, at least one length segment of the cooled intermediate cylinder is fed to a heating zone, heated to a softening temperature zone by zone therein, and, while rotating about the longitudinal axis of the intermediate cylinder, shaped into the large quartz-glass pipe having a final wall thickness and outside diameter. The quartz glass is synthetically produced and has an average hydroxyl group content of 10 ppm by weight or less. If the intermediate cylinder is divided into length segments of 1 cm, adjacent length segments have a difference of less than 2 ppm by weight in the average hydroxyl group content thereof.

Abstract: A foldable sheet of rectangular shape which can be folded by a plurality of folding edges intersecting at right-angles and by slits or slots which proceed from the center of the sides of a rectangular central portion which is surrounded by edge and corner foldable portions. In the unfolded state different foldable portions which belong partially to the front and partially to the back of the foldable sheet can be combined and to increase possible combinations, the central portion has between two opposing slits or slots folding edges intersecting at its center and one of the two folding edges of each corner foldable portion is cut to form a slit or slot, so that book-like folds can be formed in which the individual leaves can be combined by appropriate unfolding and refolding in varied ways.