GB 11p Machin Very Visible Phosphor Bands

It doesn't seem that unusual for Machin stamps to have phosphor bands that are visible to the naked eye, but, in the case of this stamp, they seem more visible than I can remember seeing before.

Is this is a sign that something went wrong in the production process?

I'm not at all comfortable with Machins, so any comments would be much appreciated.

This is quite common on some values. It looks like the phosphor bars were printed before the colour. This is known as 'phosphor under ink,' often described as 'PUI.'

Thanks for the response, NSK.

I can't tell if the stamp has any phosphor, however - despite presence of the bars at either side, it has a matt appearance across the whole face of the stamp, which I personally find very attractive.

I would describe it as a two-tone strawberry-coloured stamp.

Does this description make any sense?

It was printed from one colour cylinder (nr. 4) in pastel red and made available around November 1978.

The paler colour on each side is caused by the phosphor ink used to print the side phosphor bars. It is not a different colour. The printing is not different (same depth and screen) from the background at the centre of the stamp.

Thanks for the clarification, NSK. The result is very distinctive and, as I say, pleasing.

I try to identify machins to the level of the Stanley Gibbons concise catalogue and I notice a lot of the stamps have phosphor visible with little or no effort to the naked eye. I do wonder if the pre decimal machins have a phosphor that is becoming more visible as time goes by.

The pre-decimal Machins, like the later Wildings have the same Lettalite B3 (violet) phosphor bars as the decimal Machins up to the end of the 1970s had. The phosphor bars show better on some colours than on others, but the pre-decimals do not have a different type of phosphor ink from the early decimals.

It does happen that collectors remark they think the bands become more visible over time. I cannot say I see this in my (unmounted mint) collection. If this occurs on used stamps that have been soaked, it would be possible that there is some chemical reaction.

Here is an interesting post by the Toronto Stamp Club that shows this same variety and quotes the Deegam Handbook explanation of how it occurred: the use of the press that printed the phosphor bars for printing the Machin image as well. The press used to print the Machin image was being used to print special stamps.

http://www.westtorontostampclub.org...n_201405.htm

NSK - excellent pointer. Guess I should get a copy of the Deegam catalog. The presentation about phosphor band types was also good.