Many but not all the printings of the bicolored stamps of Denmark were printed in sheets of 100, two at a time. You may call them an A-sheet and a B-sheet. Depending which printing we are talking about all stamps in a sheet can have either the normal frame or the inverted frame as shown in my post below.
In certain printings one or a few clichés were turned 180 degrees. For what reason this happened is still being debated among the specialists. Anyhow, the result is that in certain printings you find 99 stamps with the normal frame and one stamp with the inverted frame. Or the opposite; in certain sheets you find 99 stamps with inverted frames and 1 stamp with a normal frame. This one inverted or the one normal frame is named ”an isolated frame”.
Most of the stamps with isolated frames have small errors and can therefore be separated from other stamps. It follows that stamps with a normal frame as well as stamps with an inverted frame can be common or can be rare depending whether they are isolated frames or belong to the great majority of stamps with the same frame in the sheet of a printing.
The five øre isolated frame shown is one of the rarest isolated frame. It belongs to Henrik Mouritsen.
A follow-up question:
In some sheets there are more than one that are different from the majority of stamps in the sheet. Are they also called “isolated frames”? And can normal frame also be isolated frames?
This question has more to do with language than with the way the stamps were produced.
The concept of “an isolated frame” encompasses the situation when there is more than one or several frames in a sheet that are different from the majority of frames. I cannot tell where the balance tilts - “the fifty-fifty situation” - but never mind. Such a setting does not exist.
Take for instance the socalled ”mixed series” which includes printing 12 of the 4 øre denomination. In the one of the two sheets that were printed at the same time all frame are normal but for 22 stamps which have the inverted frame. There inverted frames are called isolated frames. In the other sheet all 100 frames are normal but one which is inverted and is of course also named an isolated frame.
If we take a look at 12 øre 3rd print it consists of 53 normal frames and 47 inverted frames which by the way are all thick frames. The term “isolated” is not used about the 47 inverted stamps. It seems that we have reached the limits of the concept “isolated”.
I think that an element of the concept of ”isolated” is that the frame in question is rare and the more of a kind that exist in a certain print the less the rarity.
The 22 inverted frames in the 4 øre print 12 (A-plate) are considered interesting because they are almost all identifiable. In addition most of them are spread out in the sheet as if all the clichés had been dropped and put together maybe a little too quickly. Finally the colors of the stamp are very similar to the colors of other printings and therefore can be hard to identify already for that reason. In that respect the inverted frames come helpful, exactly because they are inverted which help you distinguish them from stamps from other similar looking prints.
Two normal frames from the 12th printing the right stamp being position 100, the position of the left stamp still illusive.
And yes! Normal frames can also be isolated frames. A very good example we find in the printings 52-53 and 54-55 of the 8 øre denomination. In the prints 52-53 you have one isolated inverted frame in the A-sheet on position 70; in the prints 54-55 you have one isolated normal frame in the A-sheet on position 31. The whole plate with all its individual clichés have been turned 180 degrees.
Position 31 - 33 printing 54
(sold at Thomas Høiland Auction june 2007)
Actually it is not that difficult to understand the system of the bicolored, if only you get a good explanation and get the chance to see the stamps with your own eyes. But many things in life are in fact like that.
Am I right?