Greetings: I am new to this site and am seeking information about how to conserve and preserve the images on glass plates ranging from 1920s to 1880s. Some of the negatives are adhered to others. I need to know a safe way to separate them. Some of them are very dirty. Is there a recommended way to clean them that will not damage the emulsion?

I volunteer at a local historical organization where one of my tasks is to scan the images in order to preserve them and make them available to the public. The plates range in size from 4 x 5 to 7 x 9 inches, approximately.