It does not matter if the sand color is white or yellow. Above all it the sand must be lumped together much like a precious stone or a stone, and the deeper in the earth one gets it from, the better. The signs of its quality is that it is thus gathered together, that, if the stone is removed as it should be i.e. in the correct way, it forms pieces and lumps together, which demonstrates its capacity for binding, and that it the sand is not too dry. However, it should crumble in your hands. And the grain must be quite small, fine, and homogeneous. If this sand is not fine enough, you can filter it and grind it up finely either with water, or through a sieve, when it or on the porphyry. That way it loses its dryness and becomes greasy and well bound. You can mold it in a box mold or in a noyau without wadding, and try it with lead because, if it does not swell and casts neatly, it will bear out well too. Some say that fatty sands do not work for casting metal that is too hot. Artisans who undertake a big job and who want to save money do not need to crush sand and seek the curious properties of artificial sand; they have more to profit from finding natural sand that has the finest grain possible. And for a small job, they take advantage of finding the finest natural sand they can. For a smaller job, they only filter the sand through the sieve. But those who work on a very small scale crush the sand and grind it finely until it becomes impalpable, because they do not need as much sand.
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Ground wheat makes a tawny—colored powder that is quite fine and quite soft. Once this powder has been mixed, it can mix mold very neatly. Try wheat flour burned in an enclosed fire.