A method for preparing pre-reacted synthetic batches, with a low content of carbon dioxide, for the production of glass formulas, which comprises mixing stoichiometric amounts of substances, containing molecular systems of silica-sodium, silica-sodium-calcium, silica-sodium-magnesium, silica-calcium-magnesium, silica-sodium-calcium-magnesium and mixtures thereof, having reaction temperatures which do not form a liquid phase, that are selected from invariant points or from points on a line connecting invariant points of phase diagrams of said molecular systems, to complete a desired molecular formula; adding cullet to the mixture; and calcining the mixture to a reaction temperature which do not form a liquid phase and wherein the CO2 is liberated.