The dowager Duchess of Argyll said she was "absolutely amazed" to have found her tiara and other irreplaceable family jewels some six years after they ended up in lost property at Glasgow Airport.

The Duchess, the widow of the 12th Duke of Argyll, lost the pieces, valued at £50,000, after setting down her hand luggage as she made her way from London to Inveraray Castle in June 2006.

She has finally had the valuables returned after spotting her missing diamond and sapphire Cartier brooch, which was custom-made for her grandmother, in an auction catalogue for Edinburgh-based Lyon & Turnbull earlier this month.

Unbeknown to the Duchess, the jewellery had gone on to the open market after being auctioned by the British Airports Authority (BAA) once the three-month maximum storage period had passed.

The items were bought by a Glasgow diamond merchant for around £5000, with the money distributed by BAA to charity.

The Duchess, mother of Torquhil, 13th Duke of Argyll, said: "I am absolutely amazed. I thought that after six years I'd lost them forever. They were absolutely irreplaceable, so I'm incredibly delighted. The tiara was a Victorian family one, and the necklace was given to me for my 21st birthday." The Duchess contacted Chris Marinello, who runs a database of lost and stolen art and antiques, the Art Loss Register.

She said: "Chris Marinello has been marvellous. I am impressed by the professionalism and co-operation exhibited by Lyon & Turnbull, BAA, and the two jewellery dealers that handled these pieces. There was a genuine desire to do the right thing even before the parties knew the identity of the theft victim."

BAA paid around £5000 to the Edinburgh jeweller, who held the Duchess's brooch and a three-string pearl necklace, and the Glasgow diamond merchant who had retained the tiara.

A large emerald ring and a pair of pearl, pink tourmaline and diamond stud earrings are still missing.

Mr Marinello said: "The Duchess had the bag of jewels on a trolley at the airport, and all of a sudden they disappeared. We think someone may have taken them and got scared off. It was reported to the airport and the police. Three months later the airport chooses to sell the pieces. You would think that when someone found a tiara the airport may have done a little extra due diligence."

A spokesman for Glasgow Airport said: "The items of jewellery were held in lost property at Glasgow Airport. In accordance with procedures at the time, the items were sold after a period of three months and the money raised was donated to charity."

He said lost property rules changed in 2007 and all pieces handed in are now reported to the police immediately, with regular audits carried out.