In the stem department, chasing' can raise the dead.
No more than anyone else can
When it comes to discolored (usually described as "green") rubber stems, a fundamental chemical reaction is responsible. The reaction is easily referenced by anyone---it's called "oxidation" or "rust" by the general public, and "redox" by the science-minded---but reality is endlessly disregarded/ignored by many PipeWorld citizens in favor of Secret Information of Unknown Origin. It's like the PipeWorld's version of the Flat Earth Society.
Ebonite/vulcanite turning green is a chemical process that alters the material at an atomic level
and cannot be reversed. (Theoretically, in a laser-equipped lab, one molecule at a time, yes, the same way lead can be turned into gold, but nothing
remotely practical under real-world conditions, never mind a pipe workshop).
The only way the oxidized ebonite can be functionally returned to its original color is to physically remove the discolored surface layer by scraping, sanding, or chemical means until unoxidized material is reached.
Chemical means is wasted effort since it leaves a pebbled, textured surface that must be scraped or sanded back to level anyway.
The end.
No magic, no secrets methods, no secret chemicals.
The closest thing to an instant fix is stain or dye. While it can work acceptably on things like old radio cabinets, on pens, telephones, or pipe stems---objects subject to handling wear---all you get is a mess.
As for the rims of pipes looking new again with spit and a rag, while there are some instances where it will work, in many cases it will not. It entirely depends on what needs to be removed. If it is built-up hard carbon that has discolored the finish or darkened the wood beneath it, stronger measures are required up to and including reconstruction (topping and refinishing).
That's easy!
