Optical dating, also known as optical luminescence, is a way to date certain materials that have been exposed to sunlight.

If I understand it correctly, it's like a glow-in-the-dark toy. Put it out in some light, turn off the light, and then it glows. It slowly fades out, perhaps in an exponential manner. If you can measure exactly how bright it's glowing now, then you can get a pretty good idea of when it was saturated with glowiness.

Now I'm not sure exactly how it works, but other materials have something much like light-memory. However, they release their stockpile of light at a very slow rate. Even fresh out of sunlight they would be pretty dark, yet a thousand years in the dark later, they might still be glowing at a comparable level.

So, if you find an artifact hidden away in some dirt, you can check out how bright it is right now. Just like with radiometric dating, you extrapolate the current level into the past, and at some point on the curve you've got it glowing like it was just in sunlight. That should be the time that it was buried!

Of course, the situation might not be so perfect in some cases:

  • What if the object never was exposed to full daylight?
  • What if it took a really long time to be fully buried? Did it recieve partial sunlight at some point?
It would seem that these two things would disrupt the conclusion. Perhaps there are techniques that can correct for these phenomena?