During an examination of some of the £1-50 "Gold head" castle stamps first issued in 1992, I noticed that two specific inks had been used to print these stamps, some examples apparently had been printed with an ink that gave off an orange reflection under UV light whilst others appeared to be of a yellow/lime green shade when introduced to long wave UV.
This finding was quite a surprise as I had not heard of it before, giving rise to a possible variety being easily identifiable under the right circumstances, here are examples of my finding of the two inks that have been used to print this particular value. >


Without the use of a longwave ultraviolet lamp I would not have discovered the differences found. WM