New South Wales postal fiscal on piece large queen victoria stamp duty on piece

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a ten shilling fiscal stamp postally used. I dont know much about this tho' I believe an act in 1884 allows fiscals to be postally used. I believe the date of issue of this stamp is earlier so it is possible it could have been used in the 19th century to produce a philatelic item for collectors. You must make up your own mind. I found this piece in a small lot with several other NSW fiscal (stamp duty ) items postally used on piece often with cds from 1894-1897. This stamp also appears to have a very faint pen cancellation just about visible from the scan
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I do post to Australia