How do you clean off the buildup of furniture polish?

French polish is a solution of the shellac in methylated spirits ( denatured ethyl alcohol). This is applied first by brush usually and then many layers with a cloth and finally rubbed with more and more linseed or vegetable oil on the cloth. After much work a mirror finish can be achieved. So removal merely meaqns washing well with spirit and brushing that into the grain with an old toothbrush for example. There are proprietary gels which can be used, such as Rustins Varnish Remover, but they are more necessary for paint like varnishes.