Great Britain (Scotland) #S5 1/3d Green Queen Elizabeth II, 1958-67 Wilding Issue, Multiple Crown Watermark, A Single Usage on a Very Fine Cover to Mexico, With Enclosure, August 4, 1964
A very fine cover to Mexico City, Mexico, sent from Glasgow on August 4, 1964. Franked with a single 1/3d green Wilding, most likely the cream paper, based on the dull reaction under UV, paying the single ounce airmail rate to Mexico. No backstamps on back. Contains a letter written in Spanish and a small sheaf of newspaper clippings advertising jobs for lecturers at local universities, which is an interesting twist. A scarce and unusual destination.
Our estimate of the value of this cover based on the above factors is $15. To understand how we have assessed the cover and arrived at this estimate and to gain a broader understanding of postal history collecting, I would suggest you read the article linked here. It should clarify the factors that make covers, and this one in particular scarce, and will help you to understand why we have estimated it at this amount.