Re: how are metals plated?

Thanks for your question. You seem to be trying experiments at home, which 
is great. It's how most of the most important discoveries were made! But 
I'm afraid what you have tried won't work - salt solution contains sodium 
ions and chloride ions and it has produced all kinds of reactions with 
your metals.
To plate a metal you need an electrolyte (the solution) which contains a 
compound of the metal that you want to plate with - the metal ions in the 
compound will migrate to the cathode and be reduced. You also need an 
anode (the positive electrode) made of the same metal - this is oxidised 
into solution to replace the metal ions being removed at the cathode. The 
cathode (negative)is the metal object you want to be plated. For example 
to plate with COPPER you need a COPPER anode, COPPER SULPHATE solution and 
then the cathode is steel (or whatever you want to plate)- it must be very 
clean.
You cannot easily plate something with any reactive metal. Zinc is a 
reactive metal and if you use an aqueous (water) solution then you'll get 
hydrogen produced at the cathode from the water, not zinc. You would have 
to use a molten zinc compound as the electrolyte (very hot and dangerous). 
Things are galvanised (or coated in zinc) using molten zinc and simply 
dipping the metal object into the liquid zinc. Clearly this is very hot 
and must not be done at home!
I hope that explains things.
Kevin