Once you’re happy with a stone’s color, remove it with metal tongs and set it on a metal cooling tray. If you leave the stones in at maximum temperature for very long periods, they can fade to light yellow and eventually revert to white. Keep the opening and closing of the oven door to a minimum. Thermal shock will occur if too much cool air enters the oven chamber. Expect some breakage but take steps to minimize it.
Wait until a good number of stones have turned to a desired shade. Then, shut off your oven and let it cool to room temperature by cracking the door slightly. If you don’t vent the oven, the temperature will continue to rise and overheat your stones. Simply re-irradiate and start the process all over. If you treat quartz from various locations, you’ll likely encounter this type. I found three mines in the Arasuai area of the state of Minas Gerais, Brazil that produce caramel quartz. None of the stones showed any identifying inclusions. They were presented to me in broken crystals or in cobbed form. One location produced only crystals up to 30 grams.
I irradiated and heated these stones using the milky quartz process I’ve described above. They go from opaque black to slightly transparent brownish to reddish or orangish brown. With continued heating, some eventually went pure orange. Some crystals, however, stayed brownish orange even after two days of heating. I expect they might go pure orange at a higher temperature than I could achieve with a toaster oven. One mine produced stones with a transition to pure orange. They went from black to a brownish orange and then turned a golden orange. Two adjacent mines just outside of the village of Itacambira, Minas Gerais, Brazil produce quartz of widely varying colors. These stones range from golden and neon green ( l imon ) to bicolors and tricolors of golden and black or brownish. Both mines yield very clean to flawless crystals up to about 100 grams maximum. These elongated crystals have unusual 10-sided terminations. You irradiate these as you would other quartz, but the similarity ends there. Their heating process is quite involved and difficult. Start heating them at a lower temperature of 350 ° F. This way, you’ll have the time to take out the maximum number of green ones, which are most valuable. The crystals go from black opaque to a slight transparency in the center only. The two ends will remain opaque black or slightly transparent brown or black. Unlike milky quartz, neon green quartz color lasts from a matter of seconds to a maximum of a minute or two. Therefore, you must remove these stones quickly from the heat as they change. If you delay, the centers will turn a golden yellow color. At that point, you’ll have a tricolor stone with a green center and blackish ends. If you take too long, you’ll have a tricolor with a golden yellow center. To create a strictly green product line, at the first removal step, saw or cob away the two ends. Next, put all the sawed sections of crystals, from the end away from the termination, back in the oven. Again, heat them to 350 ° F so the change from blackish will be more gradual. If you heat them at a higher temperature, like 550 ° F, you’ll have more difficulties removing the green ones before they change to golden. After you’ve finished processing the ends away from the termination, process the terminated ends. These will all have slight inclusions right on their tips. While you might have a small portion of green stones, it’s impossible to catch the green and golden together, because the green comes out at a lower temperature.
Right at the termination, you won’t get any green first. If you overheat at any step, simply re-irradiate and repeat the process. When irradiated, all milky or rose quartz will treat to various shades of yellow, from golden to canary. There is very little difference between rose quartz and clear quartz. However, submicroscopic inclusions of dumortierite create the color of rose quartz. This borosilicate mineral, usually blue or pink, contains titanium. A deposit just outside the small city of Governador Valadares, Minas Gerais, Brazil, in an area called Ganga Rosa, produces rose quartz crystals. To the best of my knowledge, only Ganga Rosa yields rose quartz in terminated crystals. These crystals can occur anywhere from colorless, to a hint of pink, to a fine rose color.
For irradiation coloring purposes, it doesn’t seem to matter if you begin with well-saturated or clear pieces. The subsequent heat treatment can vary depending on the location of the material. So far, my testing shows that quartz achieves its full saturation at a dose of around 60 megarads.