Where a party to an action has been ordered to produce a document part of which is either irrelevant to the matters in question or is privileged from production, he may, by leave of the court, seal up that part, If he makes an affidavit stating that it is irrelevant or privileged. Daniell, Ch. Pr. 1681. The sealing up is generally done by fastening pieces of paper over the part with gum or wafers. Sweet