What softens old shoe polish?

Answer 1

Shoe polish has a wax base so to soften it you warm it.

This only partly soves the problem, as the polish is still not soft enough to rub in. Some sites suggest adding some mineral turps or substitute, and I found White Spirits (commonly sold in supermarkets for domestic use) did a great job, leaving the polish at the right consistency. I added about an extra 25% by volume of spirits. When I used to just heat it, I held it over a low gas flame with a pair of pliers, but adding the spirit does create a fire hazard. I found the top of an oil-burner (over a tea-light candle) was very safe and effective. I think you could use the lowest setting on an electric stove.