Which treatment involves immersing opal in concentrated sulfuric acid?

The treatment involving immersing opal in concentrated sulfuric acid is commonly known as sugar treatment. This method is used to enhance the color of opal by introducing sugar into the stone, which is then carbonized through heating or treatment with sulfuric acid. The process allows for the formation of carbon deposits within the opal that can enhance its color and overall appearance.

Understanding the purpose of sugar treatment is crucial in the gemological field. It emphasizes how treatments can modify the physical characteristics of gemstones, including opals, to make them more visually appealing while also highlighting the importance of accurately identifying and disclosing such treatments in the marketplace. This knowledge is fundamental for anyone working with colored stones, as it influences both valuation and ethical sourcing practices within the industry.