if real gold, use hrwekry cleaner.!
If junk, forget it
I sell a lot of jewelry on Ebay. I use a dab white toothpaste (not gel) and a damp toothbrush. For large items I use a damp cloth. Spread the chain on a towel. Gently brush the chain in one direction letting the toothpaste foam up. Then just rinse and dry. Also works on copper, brass, silver, gold. porcelain, ceramics, sneakers, plastics, etc. For my sales I needed one product for cleaning everything.
My Gram always used dry bread . The chain usually is dirty from oils from the skin and she pulled the chain through the crusty bread. She said it worked like a charm. I have used it on my thin chains and find home made breads usually work best.
Use a solution of one part ammonia and six parts water; place your gold in it overnight and rinse well the next morning. If any crud remains, scrub with a soft toothbrush. It will be sparkling and bright.
Caution: do not do this with silver or jewelry with stones other than diamond, sapphire or ruby.