Silk is sold by weight.  “Weighting” is a textile manufacturing practice peculiar to silk manufacturing and involves the application of metallic salts to add body, luster and physical weight to silk fabric.
The reason for adding metals to silk fabric is to increase the weight of the fabric and, because silk fabric sells by the pound, the extra weight increases the selling price of the fabric. Generally, only the finer and more expensive reeled silks are weighted rather than the less costly spun silks By means of weighting the manufacturer can increase the weight of silk by 3 to 4 times.