The most well-known are the Mexican fire opals - also known as Dragon's Breath. These beautiful glass stones have mixtures of red, orange, and yellow colors. When light passes through these transparent glass stones, streaks of blues and purples are seen. This characteristic is achieved when the glass artisan adds various metals to the molten glass as it is being made. In fact, the name "Dragon's Breath" originated because of the blue and purple "breath" inside the reddish orange glass - giving the illusion of a dragon's breath. The first picture below is a Mexican glass fire opal set into an antiqued silver setting.
Glass fire opals are also made in other colors such as topaz, amethyst, blue and green. The second and third pictures are some examples. This topaz fire opal has a rich warm mix of gold, amber and topaz colors. The amethyst piece is an electric mix of pinks, purples and golds.