NOVELTY - Use of a glass to make a tubular solar collector, is claimed, where the glass is arranged to make a glass-metal joint, and the glass has a composition comprising sodium oxide (Na2O) (5-8 wt.%), potassium oxide (K2O) (0.1-3 wt.%), calcium oxide (CaO) (0.1-1.5 wt.%), aluminum oxide (Al2O3) (5-7.5 wt.%), silicon dioxide (SiO2) (70-75 wt.%) and boron trioxide (B2O3) (11.6-13.7 wt.%).    USE - The glass is useful for making a tubular solar collector (claimed) having a glass-metal joint. The glass composition is useful in glass-metal weldings, preferably iron-nickel-cobalt alloys or molybdenum alloys.    ADVANTAGE - The glass: provides good glass-metal joints for the objects, such as X-ray tubes; provides high versus transparency and transmittance; shows better stability to the cyclic thermo-mechanical actions; and provides a higher glass lattice stability, and resistance against fracture in case of thermal fatigue. The glass composition maintains the chemical physical characteristics at optimal level, and provides improved thermo-mechanical behavior.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a glass tubular container that is adapted to make a tubular solar collector, comprising a tubular glass body and parts of metal connected to the glass, in order to provide a direct glass-metal joint;    (2) a glass composition of a tubular glass body of a tubular solar collector, that is adapted to make a glass-metal joint, comprising a borosilicate glass, where the glass has a soft-segment glass transition temperature (Tgc) less than the hard-segment glass transition temperature (Tgh) for a temperature difference ( Delta T=Tgh-Tgc) higher than 20 degrees C, preferably higher than 40 degrees C; and    (3) making a solar collector having a tubular glass body that is adapted to make a glass-metal joint, comprising: choosing a metal support having a predetermined dilatometric chart, prearranging a tubular glass body, where the tubular glass body has a predetermined hard-segment glass transition temperature Tgh, a predetermined soft-segment glass transition temperature Tgc and a predetermined melting point, making the glass-metal joint between the tubular glass body and the support, heating the joint up to an annealing temperature beyond the hard-segment glass transition temperature Tgh of the glass but below the melting point, holding the joint at the annealing temperature for a predetermined annealing time, cooling according to a predetermined cooling chart the joint below the soft-segment glass transition temperature Tgc, where the annealing temperature, the annealing time and the cooling chart are chosen such that the tubular glass body has a soft-segment of the dilatometric chart as far as possible coincident to the dilatometric chart of the metal support.