Patina is primarily the mellowing and color change that occurs in wood over time due to oxidation from exposure to air and bleaching from exposure to light. Secondarily, patina is the dings, scratches, rubs, etc., that give old furniture character.
The mid-nineteenth-century cylinder roll-top desk in the accompanying picture has patina, primarily the bleaching of the mahogany and also the bleaching of the plaster-of-Paris used to fill the pores. The desk has never been refinished, but the finish has been renewed with French polishing. Adding finish on top doesn’t change the coloring of the wood underneath.
Patina is highly valued by antique dealers and collectors because it helps establish age, and it can also produce a warm, mellow appearance as with this desk.
Paint stripper based on solvent alone rarely removes patina because most of the patina is in the wood, not in the finish. But sanding will remove the top surface of the wood and destroy the patina. This is the reason old furniture shouldn’t be sanded when it is refinished.