12c Blackish Violet (162).
Horizontal pair centered to top, used with 1c Ultramarine and 3c Green (156, 158),
all tied by bold target cancels, no origination datestamp but likely Richmond Va. based on the correspondence, on 1875 cover to Buenos Aires, Argentina,
red "New York 1.10 Jul. 29" credit datestamp (stating the credit in centimes, equivalent to 22c) and red London Paid transit datestamp (Aug. 9) which ties stamps, Buenos Aires receiving backstamp, 1c stamp with small scuff in margin at top, Fine and attractive cover overpaying by 1c the 27c British Mail rate via England (the rate before July 1875 rate was 28c)
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