A major collection of west African covers and stamps from former president of the Royal Philatelic Society John Sacher is to auction at Spink.
The auction takes place in London on December 13.
All date to before 1874, when the Universal Postage Union (UPU) was established.
The UPU simplified international postage by standardising rates and reducing the need for multiple stamps from different countries.
Prior to this arrangement, sending mail overseas would often necessitate calculating the postage of individual legs and the use of mail forwarders.
The star lot of the sale is undoubtedly an 1854 cover sent from Cadiz to Buenos Aires via the British Post Office.
It displays two Spanish 6c carmine pairs and a Spanish 6r blue.
All have been cancelled with the Parrilla (grill) stamp, while another stamp notes the cover was "Paid at Tenerife".
It's expected to make £15,000-20,000 ($18,589-24,785).
An 1867 cover sent from Liverpool to Baltimore via Buchanan, Liberia carries a similar estimate of £15,000-18,000 ($18,589-22,307).
It displays a pair and a strip of three 1860 first transfer Liberia stamps, along with the various datestamps telling the story of the envelope's journey.
Spink describes it as "an extremely rare and important cover."
You can check out our incredible collection of rare stamps and covers here.
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