Intense studies and lab research has shown that mammoth tusks that were frozen in clear waters resulted in white ivory even after polishing and cutting has been done. The large crosshatch pattern or Schreger lines are clearly visible in mammoth ivory as compared to the inherent patterns on elephant ivory.
For minerals colors to seep in from the soil to the ivory takes at least 10,000 years and when you see a dark piece of ivory or hues of colors on the outer mammoth tusk, know that it has been there for a long, long time. The darker the color and penetration to the inner layers means that it has been buried in mineral rich permafrost for the longest number of years.
Another way to date mammoth ivory is by the hardness levels. Considering that mammoth ivory is not fossilized due to the fact that the core element still remains ivory and have not been replaced by minerals that lead to petrification, it can be carved. With the minerals of the soil in which the ivory is buried work up the ivory a few millimeters over thousands of years, dating colored ivory is easier than before. But if the permafrost melts and the mammoth tusks are exposed, the ivory dries up quickly and becomes useless and flaky. This is due to the exposure to direct sunlight which robs the ivory of its inherent moisture and temperature difference leads sudden brittleness. Usually ivory is dried very slowly and that stops it from crumbling.