Details
unmounted mint Block of Four -- 14p. grey-blue, variety "crystaline phosphor" in a block of four which has a very rough surface, unmounted mint
Special notice
VAT rate of 17.5% is payable on hammer price plus buyer’s premium.
Further details
These stamps exhibit a long wave reaction, similar to JET phosphor. It is believed that these were an unofficial trial by the Post Office to obtain a coating which could be continuously irradiated with u.v. without suffering loss of phosphorescence