What is the purpose of the sugar treatment in opal processing?

The sugar treatment in opal processing is specifically aimed at darkening the opal and enhancing its play of color. This technique involves immersing the opal in a sugar solution, which allows sugar to penetrate the stone. When the opal is subsequently treated with sulfuric acid, a caramelization reaction occurs, resulting in a darker hue and making the play of color more vibrant and pronounced. This enhancement not only improves the visual appeal of the opal by intensifying its color but also serves to create a more striking contrast with the iridescent play of color that opals are valued for. The process does not alter the chemical composition of the opal or significantly modify its physical durability, making the darkening effect the primary purpose of this treatment.