A French webmaster, specialist of phosphor bands on French stamps, get the lucky right to visit Phil@poste Boulazac. He discovered at the French philatelic service's printing plant, near Périgueux in Dordogne, why there have been less and less stamps with missing phosphor bands these past months.
His written summary on Les News du Phospho was posted on his blog Wednesday 9th and the commented pictures of the TD6 press yesterday Thursday April 17th. An ultra violet lamp has been added at the end of the printing press to check if the one or two bars on each side of the stamp illustration are still printed (ink in the tank) and on the right places (not 0 or 3 bars on the same priority stamp).
He noted that this new tool is part of an improvement in order to get a stronger ISO standard of quality for the plant. Important indeed because if Phil@poste Boulazac has a monopoly in France, it is in competition everywhere else. The retirement of the faulty TD215 press helped a lot too.
It stopped what was an old joke among phosphor band collectors: complete sheets of stamps missing or with ill centered bands reaching post offices and ordering clients, or even rejected sheets that illegally succeeded to exit the security plant and being sold on the French philatelic market.
In addition to his regularly updated blog, you can check this French specialist's website over here, with a side in English. Note that phosphor bands can be found on Marianne definitive stamps, but also on self adhesive illustrated or gummed commemorative stamps of France.