Gooey stuff on finished print?

Latest exhibition I went to with Sally Mann, I watched a documentary about her. She made huge prints and then covered the dry prints with some gooey stuff and scraped it off, why? What is it? Anyone?

I haven't seen the exhibition, but is it perhaps varnish? Applying that to a fiber print can give the appearance of deeper blacks (same effect as resin coating) and protect the print's surface. I think it tends to yellow over time though, I think that is an issue with some of Strand's work.