Hiya LM, any chance of posting a scan of this £1 whiter variety of paper that you have discovered, alongside a cream one front & reverse for comparison ?
This is just an example of a frontal view showing the difference between cream and whiter papers under long wave UV, in this case it concerns the 4d Guernsey plain, as according to the SG specialised catalogue the cream paper does not exist.
With a view of the same stamps in the visible spectrum, even then the cream paper appears to have a more yellowish tint when comparing it to the whiter pair.
(823.66 KiB)
According to the experts the whiter paper was produced by means of filtering the water obtained from the local river, but in my opinion these cream papers had nothing to do with filtration and was created by the use of chemical oxidation whilst the paper was still in the pulp stage, in order to nullify fluorescent contaminants that had been discovered.
WM.