During the 1980-90-ties, the stamp paper was changed from having an
"OBA"-coating (Optical brightening agent) that gave a strong white
reaction from the front when lighted with an ultra violet lamp. Due to
the belief that this coating might be detrimental to the ozon layer, the
paper producers tried out other types of coatings while still
maintaining the demand for sorting mail by various phosphor patterns.
In Ireland this development took place with the Architecture set and
continued with the Heritage & Treasure set in the 1990-ties. The new
coating named "chalk" by Stanley Gibbons, (contrary to "normal" paper)
reduced the OBA-reaction considerably, but still some reaction from the
fluorescence contained IN the paper was possible to see, and no coating
was initially used on the rear side of the stamps. This change also took
place among the commemorative sets. (The development concerned gummed
stamps, adhesive types appearing later, are an other issue).
From 1992 onwards the coating was improved and a type was also applied
under the gum. This type was more efficient and gave no OBA-reaction
from neither face-nor back side of the stamps. The Enschedé-set from1995
is a typical no-OBA type.
In paralell with above development, some printers still used OBA-paper,
thus giving the collectors possibilities of separating stamps into three
main categories, easy to separate by UV and independent of the presence
of gum (UM-stamps or used/off-paper items). Some stamps are very
expensive, dependent on the type of coating applied, but look the same
This difference are practically never expressed by sellers on Delcampe
and even the stamp catalogues do not separate the two types with poor/no
OBA-coating from each other, although it's easy with use of UV. I am not
able to determine who is fooling whom, but it does not improve the
interest for the hobby.
After 1992, the main categories became OBA and non-OBA and lasted until
the framed Bird-sets were issued, and the non-OBA became the rule.
For the sellers wanting to separate obove sets, CCP1 can be used for
OBA, CCP3 for poor OBA and CCP3a for non OBA.
Starting with the non-framed bird sets in 1997, the CCP3 can be applied
for the non OBA type.