Quartz purity is monitored using infra-red (830nm) stimulation within the standard dating procedure.
Water within the soil has an attenuating effect on the ambient radiation.
The corresponding Equivalent dose is calculated by reading it down to the x-axis. where there is still scope for much more charge accumulation) the interpolation is simple as illustrated in Figure 1a.
If the sample is relatively old then the interpolation of the natural value is at relatively high positions on the OSL axis because it is near a state of saturation as illustrated in Figure 1b.
The method is routinely applied to sediments as old as 250Ka and, consequently, is ideal for dating material beyond the range of 14C dating (A short length of undisturbed core is sub sampled in a dark room to extract a few grams of sediment.