Hobbies And Interests
Books
Don't opt for one of the many general introductions to antiques--any dealer worth his salt will have dozens already. Instead, select an authoritative book on a particular subject such as "Tiffany Silver" by Charles H. Carpenter or "M. I. Hummel: Figures, Plates, Miniatures and More Price Guide" by Robert L. Miller. You will need to know his interests and what he'd like to learn the most about to help pick the right tome.
Diamond and Gold Testers
Why not make the antique dealer's life easier with an electronic diamond tester? Costing around $70, they are the size of a highlighter pen and extremely simple to operate. Or how about a gold-testing kit? Most contain a variety of acids which react differently to gold of various carats, but there are now also electronic gold-testing kits on the market.
Jeweler's Loupe
Every dealer should have a 40x magnification jeweler's loupe with an LED light to better examine hallmarks, prints and painted ceramics. Two-lense eyeglass-style versions are also available, although the single loupe remains by far the more popular.
Ultraviolet Flashlight
Long-wave ultraviolet is useful for differentiating between gemstones and glass (because gemstones fluoresce and glass usually doesn't) and also for detecting repairs and later additions to paintings. A light, portable long-wave U.V. pen flashlight would make a fine gift for an antique dealer. U.V. flashlights can be found in most stores that sell home security equipment, but do make sure that you are buying the long-wave version.