Wikipedia sums up what it is very succinctly. “The stonework, after the work is assembled loosely, is glued stone-by-stone to a substrate after having previously been "sliced and cut in different shape sections; and then assembled together so precisely that the contact between each section was practically invisible". Stability was achieved by grooving the undersides of the stones so that they interlocked, rather like a jigsaw puzzle, with everything held tautly in place by an encircling 'frame'.”
The most commonly used hard stones were things like quartz, chalcedony, agate, jasper, granite, and even petrified wood. The artists were looking for stones with shading variations and striations to use as the coloring of the image.
Think of the many hours it took an artist to conceive of the image, cut each stone, fit each stone together like a puzzle, glue the back of each stone in place then create the metal around it to provide the friction to hold the puzzle pieces together.
But Jewelry, like art, is so subjective. If you like the image, or the contrast, or the colors of a piece, then buy it! This is your wear-able art and you should revel in it!
This brooch only uses shades of about 3-4 colors, but I’m nuts over it and would scarf it up in a second! The shading on it is amazing.
A note to collectors: Remember that during the 1950’s, we went through a sort of Victorian Revival and a lot of Peitra Dura was being reproduced. They were not fit together in that tongue and groove system like their earlier counterparts, but rather just glued onto a backing. They are still lovely and there’s no reason to NOT buy something you love. Just make sure that the seller tells you what time period the piece is from.