Performing a jewelry appraisal takes special skills.  An appraiser should have formal training as well as practical experience in evaluating and pricing similar items.

Gemological knowledge is the first requirement.  Each gem has it own physical properties or clues that a trained gemologist uses to determine the species of gemstone.   Once gemological knowledge is applied to identification, a second step is performed.  The appraiser applies appraisal methodologies to establish value in a specific market.  For example, if the function of the appraisal is obtaining insurance, the appraiser must establish how much it would cost to the replace the item in a similar market from which the item was originally purchased.

If of the other hand, the function of the appraisal is to establish tax liability for an estate, the appraiser must establish the Fair Market Value in the most common and appropriate jewelry markets.

I recommend you look for an appraisers who is associated with one of these professional organizations: