When it comes to hand wash detergents, opt for products that do not contain preservatives and leave minimal residue, especially if you're dealing with delicate fabrics like cashmere. Using a small quantity, typically around two teaspoons per several gallons, minimizes any leftover substance. For heavily soiled items or vintage clothing, rely on pure sodium per carbonate, also known as oxygen bleach, for effective cleaning. Unlike conventional detergents containing builders and fillers, pure sodium per carbonate is ideal for soaking and restoring fabrics without unwanted additives.