 So there are three properties of rock crystal that make it particularly desirable in works of art. One is the fact that it seems to pick up and reflect and magnify the light that hits it. And I think you can see that particularly in some of these examples here as they pick up the light and sparkle, it also, since it is clear, takes on the color of the things that touch it. And we're going to see a work of art that was meant to be held in the hands. And you'll notice that this goes from being sort of celestial and clear and ice-like to suddenly being warm and flesh-like when I hold it in my hands. Similarly, if I take the crystal and put it up against my scarf, you can get a sense of the color of the scarf through that crystal, and it affects it. It changes the color of it. The other thing that is really remarkable about rock crystal is it has some magnifying qualities. And you can see that pretty nicely with this crystal here, which has some nice facets in it. If I place it on the text, you can see how the text appears larger. And that can be used to, it was used particularly in medieval reliquaries, to make the relic behind the crystal appear larger to the viewer. So, for example, think about having a very small piece of the true cross and how the crystal properties would attract light to that relic and also seem to magnify it for the viewer. And this would enhance their religious experience.