The common cause of silver surfaces tarnishing is due to exposure to Sulfur compounds, either in food or as trace sulfide fumes in the air. Aluminum foil + baking soda cleans silver by an electrochemical reaction. The silver sulfide is reduced back to silver metal by electrons flowing from the aluminum to the silver, and as this can only happen at the silver surface, the recovered silver plates back onto the surface. This is only effective for high silver content alloys and plate, and the method is not recommended for any silver alloys lower grade than Sterling silver (92.5% Ag).
Tip tinner/cleaner 'cakes' are usually a mixture of solder powder (nowadays Sn97/Cu3), Ammonium phosphate, a mild abrasive such as diatomaceous earth, and a trace of flux resin as a binder. On heating, Ammonium phosphate decomposes to ammonia, which gasses off and Phosphoric acid, which reacts with metal oxides on the tip forming metal phosphates and also polymerizes at high temperatures, forming a low volatility acid fluid which carries away the metal phosphate residue. The solder component of the tip tinner cleaner (hopefully) immediately re-tins the exposed metal. The high copper content of the solder minimizes its tendency to dissolve the copper core of the bit at any cracks or pits in its iron plating.
Its therefore obvious that tip tinner/cleaners in use are similar to strong acid flux. If left on the tip, the residue from both will rapidly corrode it so its essential to thoroughly wet clean the tip, after restoring it with a tip tinner/cleaner 'cake', then re-tin it with solder and non-corrosive flux.
Contact with plastics is problematic as PVC and some others decompose, producing hydrogen chloride (or other halides), which rapidly attacks the tip's plating. If you wipe off melted/burnt plastic immediately before its removed all the tinning from the tip surface, wet wipe and re-tin, you'll have much less trouble. Leave it to char and the tip will probably be permanently damaged.