there are lots of things that you have to look out for when dating gold jewelry. First of all is the jewelry hallmarked?
If it is hallmarked these marks will help you date the age of the gold jewelry. Countries all have different hallmarks though. There are thousands of hallmarks :(
If you can work out these marks it makes the job of dating your jewelry easier though.
If the jewelry is not hallmarked you have to look at other things. Here are a few - 1. The gold work techniques used in conjunction to regional areas 2. Does the jewelry contain gemstones, what are they, how are they cut? Are the gemstones the originals or later replacements?
3. Look at the condition. Are there visible signs of age?
This page about Antique Jewelry Buying Basics might help too Sunil.
