to retain heat therein application_number US 53104883 A description in metal casting in a sand mould an exothermic heat retaining agent 3a of the invention is located at a holding cavity 6 of a blind riser 2 within the mould before a cope 4a and a drag 4b are assembled additionally depending on the configuration of the mould it is possible to locate said heat retaining agent 3a at the cavity 6 of the blind riser even after assembling the mould in the drawings reference numeral 1 designates a sprue and reference 5 a main mould cavity of the mould the thus obtained heat retaining agent for the blind riser of the invention can be used being simply placed at the cavity 6 of the blind riser 2 of said sand mould this method can be easily carried out at the optional period of time before the cope and drag 4a 4b are assembled in the moulding process of the mould and according to the casting plan to be applied for example in case there exists an opening to the outside of the mould which opening is communicated with a position expected for placing the heat retaining agent it is possible to place it even after assembling the mould it is possible to select the placing position of the heat retaining agent 3a at any place such that said agent 3a will be positioned 3b at the top of the blind riser when the pouring of the melt has finished after said agent has.