Sometimes, the denomination on a common stamp from a series has been changed to a rare denomination. Has an overprint been added or removed? Has a cancellation been added or removed? If the stamp is cancelled, is the cancellation genuine and of the proper period for the stamp? Has a grill been pressed out? Used grills of the US 1869 Pictorial Issue can be pressed out to appear to be 1875 re-issues. Have other changes been made? The common 4 annas bicolor stamp of India has been altered by cutting out the image of Queen Victoria and remounting it upside down, or by chemically erasing the image and reprinting it upside down, to make the stamp appear to be the rare invert. Experts will also attempt to determine whether genuine stamps have been repaired or cleaned: Has a tear been mended? Has a missing piece been restored? Has a thin spot or hole in the paper been repaired? Has the stamp been cleaned? Has the stamp been regummed? Have short or missing perforations been repaired? Has a crease been repaired? Covers Among the factors experts may consider for a cover are: The cover itself: Are there any repairs to the cover Sealed tears Stains removed by bleaching Cutting down one side of the envelope to remove a torn edge where the envelope was opened Erased pencil marks written by earlier stamp collectors Is the cover faked: Is the paper from the time period when the cover went through the mail? The stamps on the cover: Are the stamps genuine or forged? Are the stamps correctly used? For example, using a stamp years after it is no longer valid for postage Have the stamps been repaired (cleaned, bleached, reperforated)? Have the stamps been removed from the cover and reglued to it? Usually done to identify rare varieties of the stamps Have stamps been removed from the cover? Have stamps been added to the cover which were not present when the cover passed through the mail? For example, adding a rarely used stamp to an existing cover to make an ordinary cover extremely valuable Have the stamps been removed and replaced with different stamps? For example, removing a stamp in excellent condition and replacing it with one having damage to the back, giving that the damaged backside of the stamp will not be visible. The postal markings on the cover Are the