During a session of soaking off some Harrison Machins, I noticed after using tissue paper as a source for drying them that the tissue had become impregnated with a fluorescent substance, and could only presume that the fluorescence had come from the surface that the stamps and been initially coated with, concluding that this fluorescent substance was highly fugitive once moistened and could easily contaminate the stamps in soak.
This is the tissue in question and my observation under UV as to it's condition after use, here is an attachment attributed to that fact .....,

After seeing the tissue, I then decided to examine some of the stamps, again under longwave ultraviolet light and discovered that they had also been affected by their coating once submerged in water, as can be seen in the next attachment.
Is there a way to prevent this from happening other than by sweating them off individually ?
Another important question is "Was the substance used toxic" ? WM.

WM,

QV surface-printed stamps have very fugitive ink, but it never occurred to me that there might be a problem with the coating of early decimal Machins, not just to the stamp being soaked but its companions in the soak.

Would floating them face up on the surface of the water, letting the water seep through from below, with individual rinsing, reduce the problem to acceptable levels?

As to toxicity, I would not have thought there was any, even though H&S was not so important almost 50 years ago. Or if there was, not enough to harm humans. But best perhaps not to let your dog/cat/fish drink/swim in the residual water.

Regarding toxicity: while I don't have data on this specifically (other than a general recollection that toxicity was one reason for not using inorganic phosphors), I did come across a c.1970 report in the PO archives analysing the gum on some registered envelope flaps that contained a trace of arsenic.

The conclusion there was that it wasn't remotely enough to cause a problem even if someone licked lots of them, but it was certainly enough of a concern that they were testing the gum. So I expect that any substances used as phosphors were tested for toxicity beforehand.

Good morning Winston,
Your method of soaking off in order to prevent contamination occurring sounds helpful and I could add that the stamp be removed from it's paper ASAP once removable.

I suppose that by now millions of these stamps from this particular era will have already been processed and their owners are unaware of their condition, especially if they don't have a longwave 'black light' to hand.

It would be interesting to hear from other collectors with similar attributes on this particular topic.

Thank you also Moz regarding possible toxicity of gum.

Perhaps due to some of the factors mentioned the self adhesive was introduced on October the 19th 1993 and fluorescent surfaced papers are no longer produced due to changes in technology and possibly environmental aspects as an improvement.
But even then with their new technology, the Royal mail still have to rely on the postman to cancel some of their mail ! What a farce, WM.