PURPOSE: To prevent a cutting oil from decomposing or emitting an offensive odor for a long period of time at a low cost, by immersing a mass of water-soluble glass contg. Ag and wrapped in a water-permeable fiber cloth in a cutting oil or the like diluted with water to elute Ag+ ions while dissolving the glass through gelation of the glass.

CONSTITUTION: Solid matter comprising water-soluble glass in the form of a mass, particle, a powder, or any combination thereof and composed of 100pts.wt. glass compsn. contg. at least one of SiO2, B2O3, and P2O5, at least one of Na2O, K2O, CaO, MgO, BaO, and ZnO, and at least one of Al2O3 and TiO2 and 0.1W2.5pts.wt. Ag2O is wrapped in a water-permeable fiber cloth comprising a (non)woven fabric or a synthetic resin sheet in such an amt. as will provide a solid concentration of 300W1,000g/m2. The wrapped solid matter is immersed in a cutting oil or a grinding oil diluted with about 10W100-folds as much water. This not only prevents a suspendible substance and suspended matter contained in the oil from penetrating into the inside of the cloth through the mesh of the fiber cloth and, at the same time, causes Ag+ ions to be gradually eluted outside the fiber cloth through a gelation of the glass, thereby preventing the oil from decomposing and emitting an offensive odor.