Line a nail polish brush with a thin layer of nail polish and carefully apply the liquid along the length of the scratch. Leave the polish to dry for a few minutes. If there are any smudges on the edge of the crack, wipe away using nail polish remover.
Apply jeweler's rouge to a soft buffing cloth and rub gently around the scratch. Jeweler's rouge is an organic compound that is effective at improving the appearance of cracks and scratches. Use a circular motion when applying and ensure the cloth is clean before use. Jeweler's rouge can be bought from arts and crafts stores and jewelry shops. Whitening toothpaste can be used in the same way if you can't obtain jeweler's rouge.
Mix 1/2 oz. of ammonia with 2 cups of warm water. Buffer the scratch using a soft clean cloth and the place the mixture into a spray bottle and apply to the scratch. Wipe the area clean with a lint-free cloth, to ensure there is no further damage. Ammonia can be dangerous and produces unpleasant fumes so wear gloves and safety goggles during the procedure. Never mix ammonia with any other chemical.
Contact a glass repair specialist if the scratch appears too deep and fails to respond to the above treatments. In serious cases, the glass top on your table may need to be replaced.