KT has done appraisal values for several individuals, but for collections of minerals and rocks, not for jewelry or gemstones.
One important thing to note is what type of appraisal are you asking for? There is replacement value (generally done for insurance companies), there is retail value by the piece, or there is wholesale value, which is for the sale of large collections. Retailers, whether jewelry stores, rock shops, etc., in general have large markups on their merchandise. They expect to buy wholesale and sell retail, which often involves up to a 10X markup. That way when they advertise an annual "sale" for 50% off select merchandise, they still make 5X their investment. KT has done collection evaluations, and these are for insurance purposes. When asked, if I sell the collection to one buyer, what should I expect to get by auction or sealed bid, I generally tell the seller, if you are offered 10 to 15% of my evaluation, take it. Too much emphasis is placed on sentimental value, which has no place in the retail market, although jewelers use it all the time .....remount your grandmother's old diamond, remake your old jewelry, etc.
Rock and mineral collectors spend a lifetime gathering samples, and all the fun of doing that is part of the hobby, but it adds no value to any particular piece ...the scarcity and perfection of the piece is what gives it any value, and the desire by someone else to own it!