A method of manufacturing an artificial stone slab comprising veins, said method comprising the following steps performed in the following order: a) preparing a moldable hardenable fluid mixture of a first material; b) pouring a controlled amount of said mixture of the first material into a mold of the size of the artificial stone slab to be manufactured, an upper face of the mixture deposited in the mold being exposed; c) engraving the exposed upper face of the fluid mixture with a predefined precise pattern of open grooves, coinciding with a pattern of thin veins to be obtained; d) impregnating at least the inner faces of said grooves with a moldable hardenable fluid mixture of a second material, the color of the first material and of the second material being different; e) causing the collapse and closure of the grooves, obtaining a visible pattern of thin veins of a second material with a natural look; wherein the method subsequently includes the following steps: f) curing the artificial stone slab by subjecting it to vibration, compression and vacuum until the fluid mixtures of the first material and of the second material are hardened; g) releasing the artificial stone slab from the mold; and wherein • said first material includes stone particles having a different grain size distribution; and • said step d) is performed by means of projecting said fluid mixture of a second material through at least one projecting head and by moving said projecting head following said open grooves while the mentioned projection takes place, wherein moving said projecting head is performed by means of an automated arm reproducing the mentioned predefined precise pattern of grooves to be obtained. a) preparing a moldable hardenable fluid mixture of a first material; b) pouring a controlled amount of said mixture of the first material into a mold of the size of the artificial stone slab to be manufactured, an upper face of the mixture deposited in the mold being exposed; c) engraving the exposed upper face of the fluid mixture with a predefined precise pattern of open grooves, coinciding with a pattern of thin veins to be obtained; d) impregnating at least the inner faces of said grooves with a moldable hardenable fluid mixture of a second material, the color of the first material and of the second material being different; e) causing the collapse and closure of the grooves, obtaining a visible pattern of thin veins of a second material with a natural look; wherein the method subsequently includes the following steps: f) curing the artificial stone slab by subjecting it to vibration, compression and vacuum until the fluid mixtures of the first material and of the second material are hardened; g) releasing the artificial stone slab from the mold; and wherein • said first material includes stone particles having a different grain size distribution; and • said step d) is performed by means of projecting said fluid mixture of a second material through at least one projecting head and by moving said projecting head following said open grooves while the mentioned projection takes place, wherein moving said projecting head is performed by means of an automated arm reproducing the mentioned predefined precise pattern of grooves to be obtained. • said first material includes stone particles having a different grain size distribution; and • said step d) is performed by means of projecting said fluid mixture of a second material through at least one projecting head and by moving said projecting head following said open grooves while the mentioned projection takes place, wherein moving said projecting head is performed by means of an automated arm reproducing the mentioned predefined precise pattern of grooves to be obtained.