In the late 19th century, librarians and conservationists began silking manuscripts in an effort to best preserve the materials. It was thought that this process would help strengthen the paper, making it less susceptible to damage.
Silking involved cleaning the manuscript and then applying paste and a silk gauze, sometimes referred to as crepeline, to either one or both sides of the leaf. However, it did not take very long for conservationists to realize that this was not an adequate method of preservation. Over time the silk became brittle; discoloration occurred; it could separate from the document; some silks had a rapid rate of deterioration; and silking generally "failed to render the document any more resistant to the enemies of paper" than untreated pages (William Barrow, 1939 Newport News (Virginia) Daily Press article).
Which brings us to the process of de-silking, through which the silk gauze is very carefully removed. The Morgan Museum & Library had to de-silk their manuscript of Charles Dickens's A Christmas Carol last year in anticipation for their exhibit Dickens at 200. The procedure is explained in the informative video below and is also summarized on their website.