It is stated in the Gewerbeblatte fur Hessen that paint can be renewed and refreshed in the following manner:

When cracks and checks appear in the paint on wooden articles, this usually indicates that the varnish has cracked. If this is the case, the article can easily be prepared for a fresh coat by sponging it over with strong ammonia water, and two or three minutes later scraping off the varnish with the broad end of a spatula before the ammonia has dried up.

In this way the first coat is removed. If it is necessary to remove the next coating, the same operation is repeated. After the last coat has been scraped off that is to be removed, it must be washed with sufficient water to render the ammonia inactive, and then the surface is rubbed with pulverized pumice to make it smooth. Any desired paint or varnish can be applied to a surface prepared in this way.