This brooch is marked with a Dutch hallmark, used 1906-1953.
The colourful brooch is made in a specific technique, a so-called ‘reverse intaglio’. A reverse crystal intaglio is a cabochon cut natural crystal with an intaglio carved into the flat underside. This image is painted and mounted on an opaque background (usually mother of pearl). Finally, the back is sealed with gold, to preserve the painted areas. When viewed through the front, the image appears three-dimensional.
The technique originates in Belgium, c. 1860, and is attributed to an artist named Emile Marius Pradier. His method gained popularity both in England and Austria. More information about reverse intaglio: Lang.
The Mayan and Incas believed that petunias have the power to chase away the underworld monsters and spirits with their bad smell. According to the narrative, petunias can not thrive in places of intense negative energy.
Source 1st and 3rd photo: petunia – www.gardentrends.com