求翻译：It has long been known that textile materials, that is spun yarns, extruded filaments, woven fabrics, knitted fabrics, non-woven materials and the like can be rendered more opaque by the addition of various metal oxides, such as titanium dioxide thereto. By adding opacity to a sheer textile material, the covering power of the material is greatly improved, without the extra weight and cost that would be present for a heavier, tightly formed substrate. Likewise, in so adding opacity to the textile material it is quite desirable, if not imperative, to avoid changing the handle characteristics to a point where the material becomes unsuited for garment use, for example, and the improved opacity characteristic should be retained after repeated launderings or dry cleanings.是什么意思？

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