Signity, the Swarovski-owned distributor of precision-cut gemstones has acquired the California-based producer of enhanced topaz, Leslie & Co. %% According to reports the acquisition would bring several exciting topaz colours into Signity’s colour portfolio that are enhanced through Leslie’s patented Pollak Heat Diffusion (PHD) process. %% The Leslie PHD Process is a fairly well known chemical heat diffusion method developed by Richard Pollak, initially for sapphire and ruby, whereby metal oxides are inserted into the crystal lattice structure of the gemstone.