I am NOT a Jeweller or an Antique Dealer ~ I have no qualifications in so far as Jewellery is concerned. I do have a very keen interest in Jewellery ~ Particularly 'Olde' Fine Jewellery.
I do have many Reference Books on the subject and do a lot of Research (as much as possible) on my own items for Sale
These are just a few things I have learned over the Years that may help others.
Antique Jewellery: Generally an Item of any Description is NOT classed as Antique unless it is 100 Years old or Older.
If someone is offering Antique Jewellery that has 'White Gold' in it ~ It is Not Antique. White Gold did not come into common use until the 1920s All mined gold is yellow ~ It is just the other alloys that are mixed with it to make a Colour such as White Gold. (White Gold is mixed with Silver, Rose Gold - Copper and so forth) From approx. 1920 onward, it was used extensively particularly in Diamond Jewellery Settings as a Cheaper substitute for Platinum and a harder substitute for Silver. Diamonds are set in White Metals in Preference to Yellow as the Yellow Metal makes the Diamonds appear to have a Yellow Tinge, particularay if they are not a top 'white' in Colour
Be Careful also of Jewellery that is Stamped 9Ct Gold, especially if it is described as 'Georgian - meaning 18th or early 19th Century NOT George V or VI ( 20th Century) There was no Assay mark for 9Ct Gold before 1854..
Most settings ~ Early Victorian and Georgian containing Gems were 'Closed Settings'. That is the Back of the setting was closed and you could not see the gem(s) from the back of the Piece. Foil was used at the back of the Gem to produce brilliance. Many so called diamonds using this teqnique are nothing more than quartz - so be careful make sure the 'diamond (s)' have been tested and that the seller is reputable
The Gem Cuts were also different ~ The Modern Brilliant Cut was not introduced until the early 20th Century ~ So Antique Jewellery having Modern Brilliant Cut Gems are Not Antiques, unless stated that 1 or more Gems have beev replaced - they used 'Rose' Cut and 'Old European Mine Cut' (old Brilliants, that have a very wide 'table') Gems. Any working Jeweller can identify these for you. If the Diamond are small they were quite often only chips from cuttings off larger Diamonds ~ This type od Diamond Jewellery is coming back into fashion - Particularly at the 'Chain' Stores - so watch & ask.
Pearl Jewellery was most popular in Victorian times and if you are fortunate to have a piece of Antique Hallmarked Pearl Jewellery ~ It is most likely that you have a 'Real Pearl' (a Wild Pearl ~ Strings of these Sea Pearls are worth a Fortune) ~ Not Cultured but REAL. ~ Early Cultured Pearls are also worth a few Thousand Dollars in Good Condition ~ They have a Thick Nacre and just feel and look different to the Mass Produced Pearls particularly coming out of China.
Cultured Pearls were first introduced after much trial and error by 'Mikimoto' in the late 1800s, but not readily available commercialy until the 1920s.
In Ancient times Real Pearls were the 'Most Valued' Gem. Cleopatra is said to have had the most 'Expensive' meal on Earth. She did this by crushing a Pearl and washing it down with wine. Real Pearls are still Rare and very Expensive. They can only be tested by an x-ray ~ & examined by a qualified gemologist
In Antique Jewellery you will notice that some is described as 12Ct Please be careful and read the FULL DESCRIPTION as much of it is 'fill' - this means that the gold is only 1/10th or a 1/20th part of the carat gold and is not SOLID 12Ct or whatever Carat Weight is is supposed to be. It is a cheaper substitute for the REAL thing and not worth nearly as much as Carat weight Gold , although it is a better quality than the Rolled or Plated Gold of today.
I hope this helps initially with an ebay Purchase - The best person to see after Purchase to Confirm is your Trusted Jeweller or an Antique Specialist. Don't be shy in coming back to your Seller - if Your Item is 'Not as Described' or report them to ebay if No Satisfaction is given. Most Sellers are Genuine - as with everything there are some that Spoil it for the rest
Especially ~ Watch for ads with 'DIAMONDS'?? or Rubies? ~ (with the Question Marks) Don't Touch them with a 10 foot Pole ~ Most Sellers know exactly what they are Selling - Would you put a Question Mark after Diamonds ~ OR as an Honest Person ~ take it to a Jeweller and have it inspected before listing, You could easily be giving away a Piece worth much more money too and people just don't do that.~. These items in 99.9% of cases are Cubic Zirconias - GLASS. Not to be confused with Zircons that are an Earth Mined Gem.
Be Very careful too, of Sellers who say the item has NOT been Cleaned , and found in Grannies Attic I would certainly be taking that to be inspected and tested by a Jeweller before selling. If an item containing gemstones has not been cleaned (especially if the Gems are Precious Gems) - how can they tell if they are included and what the Colour of the Gem is? ~ I read an ad ~ 5 of the Very Best Diamonds but very dirty - Needs a good clean - I did check back later and the person who paid quite a lot of money for the item, was less than impressed - the Diamonds were full of Carbon Spots and cracks NOT Dirt. I hope this is of some help and most Sellers are Honest - I must admit
Kind Regards & Happy Ebaying