Thats a good question. Accurate valuation is crucial if you're to get an appropriate level of contents insurance.
First stop for most people would be your local jewellers, or indeed antique jewellers if one is available in your region. While some will perform a cursory examination for free, most will charge a nominal fee for the valuation, if there are only one or two pieces. For larger quantities of course the fee will increase, as the time taken by the expert will naturally be greater.
There are also some online guides on how to estimate value of antiques and antique jewelry, explaining what to look for in the way of defects and imperfections, right through to establishing when the piece was first made, and by whom. This of course will hardly be as accurate as a professional valuation, but may give some indication as to which pieces you would deem suitable for closer inspection.
Who do you go to to get an independent and reliable valuation valuation of old family heirlooms, such as my great grandmothers old jewellery?