It was treated by Maisel in the 1950’s. Not exactly sure the process they used. So the value of this turquoise lies in its history. This turquoise was owned by The Maisel Fred Harvey Company and then later in the 60’s was purchased by The Sunbell Company which was The Bell Trading Post. Southwestern US turquoise history is rooted in these two companies and this history. That’s why this turquoise is special. There’s a lot of old stock turquoise out there but this is unique in that it was actually owned by Fred Harvey and Jack and Mildred Michelson (Bell Company)