 Welcome to the series, Photographic Chemistry, presented by the Foundation of the American Institute for Conservation of Historic and Artistic Works. This program was made possible by grants from the National Endowment for the Humanities and the Andrew W. Mellon Foundation. Each program in this series is presented as a short video. Depending on your video viewer, you should be able to pause, return to a previous section, or skip ahead to a later section by using a scroll bar or on-screen icons. You will find an outline of the course and short quizzes to test your understanding on the course webpage. There are two ways in which a Frankel defect can occur. A Frankel defect, which is mobile ions moving into the interstitial areas of a crystal. We can have a surface kink to an interstitial movement of silver, and this makes a net surface of the crystal negative in charge, as shown in the diagram on the right. And we can also have the opposite. We can actually have a silver move from an interstitial site onto the surface. Both of these have impact on, again, the development of what will later come to learn to be a latent image up to a silver image requires the conductivity and the mobility of these silver ions within the crystal lattice structure. There's about, and here's a little fact, there's about one defect, one Frankel defect for every 10 to the eighth ion pairs. This translates to about a dozen or so Frankel defects happening at any one given time in the silver crystal structure. I used to have a laboratory in the technical photographic chemistry class I used to teach here at RIT, where I would demonstrate this Frankel motion, by having the students take film and expose it to light in a very unnatural way. I would have them pour into a beaker liquid nitrogen, which is temperatures that reach down to about minus 290 degrees Celsius, extremely cold. This is a cold enough temperature to freeze the atomic motions of ions in the crystal. So to demonstrate the Frankel effect, I had them lay a strip of photographic film in just a pail of water. And next to it, I had them place a strip of photographic film in a bath of liquid nitrogen, liquid nitrogen is colorless, so it sort of looks like a bath of water except for the differences in temperature. And then I had them do something very unnatural, which is I told them to turn the dark room off. Which is I told them to turn the dark room lights on and leave them on for a good minute. And they did that and they turned the lights back off and then I instructed them to develop the photographic film as they normally would using photographic developer. When they were done, you could imagine the results. The film that was placed in just normal room temperature water was fully exposed and had full silver density, a full black on the photographic film surface. And the film that was exposed that was in the liquid nitrogen had absolutely no record of exposure. There was a little bit of density there, but it was almost as if that film never was exposed to light. And we're talking about room light for a good solid minute. So this demonstrates that if we freeze out these ionic motions, we can prevent the silver halide grain from even recording an exposure event. Exposures are happening and we'll talk about how this works in the latent image theory section, but ion mobility is absolutely required. These frankel defects are actually required in order to form the latent image and then subsequent to that, a silver-developed image. You have completed this unit. Depending on your video viewer, you should be able to scroll back to any point in the video as desired. The short quiz found in the course materials on the website may help you confirm your understanding of the concepts introduced here. Many thanks to the instructor, production editor, coordinator, and the collaborative workshops and photograph conservation committee for their work to make this program possible.