 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. As we've mentioned, one of the differences in the chemical adsorption properties of the sober halide grain systems is found with the absorption of the halide anion. And they trend pretty much as the KSP trends, the strongest binding halide is the one you would expect, the one with the lowest solubility, and that's the iodide anion. So the trend in binding to the surface of the grain goes as chloride being the weakest, then bromide, then iodine. And we use this, again, to our advantage if I want to restrain the development of grains and we have to learn a little bit about what a developer is, again, in a later discussion. We're going to do that with a chemical known as a chemical restrainer. A chemical restrainer is bromide iodine. It's almost always potassium bromide. This is because the silver bromide tends to be the key halide component used in 20th century products, both photographic films and papers. So we will tend to want to restrain the development of the photographic development process by using a bromide ion, because we know the bromide anion will adsorb onto the grain and creates, as we discussed before, this negative shield around the silver halide grain. It makes the grain negative in charge on its surface. And again, these surface properties are very key to photographic development. And we also understand that in the reverse, the addition of silver has an impact on the absorption of various components onto the grain. If we add much more excess of silver into the solution, then what we find is that we can dissolve the halide out of the grain and actually dissolve the grain in a controlled way into solution. This is the basis for physical development. Again, a discussion when we get more into developers how this actually works. But it's these chemical adsorption properties at the surface, which are very key. And there are differences found within each of the silver halide compounds. 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 in Photograph Conservation Committee for their work to make this program possible.