Juts taken some pic's to show you what some chrome looks like close up - it may look shinny after a polish - some times it can look a bit dull in place's - the stuff you use to polish or clean can do damage in way you can't see
surface rust is pin holes that let the metal rust and sit on the surface, and when you clean it, it will lokk shinny but you can still see the pin holes close up
Hairlines reflect light in different directions - so from a far it looks shinny and mirror like but close up you can see the lines left
different chrome/metals close up
pitting ~surface rust cleaned up
worn chrome showing where it has lost it's shine - you can't really polish it back up without taken off the chrome and going to bear metal
headtube on a mongoose - rough metal but chrome sticks to it and still can be shined up - rear gusset and rougher metal but has hairlines and marks
MX Caliper - shinny and mirror looking ~ but close up has marks and lines
Mirror polished stem - in certain light you can pick up the rainbow light reflecting in different angles
New shinny £2 coin - looks mint but close up you can see the knocks and dents - damage will only make it look dull in time
so you can see that using coke and tin foil will damage chrome and not do it well, showing scratches and lines, cos of the rust caught in the foil and as the foil gets harder and more crunched up will leave more lines and marks - using the right stuff will help make the chrome look better and give a better finish
hope this helps - cheers B