A way to show this would be to place a piece of etched glass over a flat surface with the etching facing down. Then wet the etching with either water or oil. Notice the difference in clarity.

A more permanent method of repairing optical problems in the finish would be to go about it in a different way--reconnect the finish in a more permanent manner. To do this you may want to either re-soften the finish using its original solvent (if possible), or use one of the finish re-flow products available. You may also try working some clear varnish (or other finish product) into the scratch or damaged area. Then allow this to dry. Buff to a gloss. I suggest varnish, as it will not likely soften the surrounding finish. Lacquer is much more volatile, and may upset the surrounding finish.

Doing this will permanently reconnect the finish with the wood. When you oil wood using Pledge or salad dressing or some other oil (walnut), the oils will eventually soak into the wood and pull away from the finish, and the scratch will reappear. Oils on the finish also tend to assist in further lifting the finish.

As always, experiment and see which methods you like best. There are situations where oiling the finish may be preferred to rubbing varnish into the finish. It is also good to note that waxing a finish to remove scratches is on par to oiling the finish. Thus the removal of scratches with wax may be no more permanent than with oils.

Thomas