Wood finish, unlike paint, allows you to preserve and appreciate the beauty of wood's natural coloring and grain. Many wood finishes contain fewer harsh chemicals than commercial paint. Particularly in the case of a wood item that will come into contact with food and drink, such as a cup, using a nontoxic wood finish is vitally important. Fortunately, you have several options from which to choose.
You can use a variety of natural, nontoxic oils, such as mineral oil, to seal and finish wood. Clear mineral oil will not alter the color of your wood, but it will soak into the surface and provide deep protection for your wood rather than building up on the surface like wax. Mineral oil is also easily available, sold in most pharmacies as a laxative. Simply brush it onto the cup with a brush, remove the excess and allow it to dry completely.
Linseed oil takes a good while to dry -- up to three days -- but many woodworkers find that attractive shine it creates well worth the wait. Boiled linseed oil often contains chemicals that should not come into contact with food and drink, but raw linseed oil is completely natural and provides a lasting finish along with an attractive yellow tint that can enhance the natural color of your wood. As with all oils, multiple coats will ensure greater protection, but the slow absorption of linseed oil makes these additional coats particularly important.
Derived from the nut of a tree native to Asia, tung oil makes a good choice for woods that already have a nice color, as the clear oil does not alter the color of the wood significantly. Like linseed, tung oil penetrates the wood and hardens to protect the surface. The fact that natural oils penetrate the wood, instead of forming a film on the surface, also helps when finishing cookware, as the oil will not rub off on food or drink to affect the taste.
As with linseed oil, use pure walnut oil to finish your wooden cup. Several treated walnut oil finishes contain harsh chemicals that can affect your health if they come into contact with food or drink. Walnut oil also adds an attractive dark finish to the color of your wood and provides excellent protection against water. As with all oil finishes, you can reapply walnut oil to the wood surface at any time and allow it to dry to restore the original shine and finish.