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Overview Probably no topic causes more confusion for collectors than the study of paper fluorescence. Many feel that there is too much subjectivity involved in evaluating and studying paper fluorescence and there is a tremendous amount of inconsistency among the stamps listed in Unitrade. Indeed many of the stamps listed are described as having the same degree of fluorescence, but appear completely different under the UV lamp. This makes positive identification of single stamps next to impossible for those unfamiliar with the papers, unless the varieties are unmistakably obvious. This post will attempt to explain why this confusion arises and break the topic down into more manageable components, so that you will be able to see that the study of paper fluorescence is not impossibly complex. The Cause of Confusion and Basic Grades of Fluorescence The subject of paper fluorescence is confusing because many of the papers used contain fibres in varying densities that react differently to the UV lamp than the main paper. In addition, the use of paper coatings in the early 1970's has resulted in many papers that give different reactions on the face of the paper from the back. To begin with it is important to understand the basic levels of fluorescence and what they look like: 1. Dead paper (Dead) 2. Non-Flourescent (NF) 3. Dull Fluorescent (DF) 4. Low Fluorescent (LF) 5. Medium Fluorescent (MF) 6. High Fluorescent (HF) 7. Hibrite (HB) Dead, Non-fluorescent and Dull Fluorescent Papers The picture taken with my I-phone camera shows the three lowest grades of paper fluorescence: Dead, non-fluorescent (NF) and dull fluorescent (DF). It is important for me to point out that the camera does not adequately capture the differences between the grades, dulling them. So in reality the differences between the following stamps are much greater in real life:
NF paper appears a lighter brown or lighter purple. Again it absorbs and does not really give off any glow at all. The main difference between NF and dead paper is in the depth of colour that the viewer sees. The stamp in the centre is NF. It appears darker than this in real life. But if you look closely at the picture, you can see that it is definitely duller than the stamp on the right. DF paper is the most common paper type prior to the Centennial issue. This paper type varies quite a bit in colour under UV, but generally, it gives off a very dull, bluish or greyish white appearance. It will not have the brownish or violet appearance of the NF or dead papers. It will not appear to be at all fluorescent, but compared to the above 2 types it looks quite fluorescent. It is important to note that fluorescence refers to the brightness of the reflected light, not the colour. DF paper can come in several different types, each of which reflects a different colour under UV:
These are some of the colours I have seen. The difficulty for the novice is that it is very easy to mistake the bluish white or greyish white DF paper with fluorescent paper if the person has never seen true fluorescent paper. This is especially the case if you are used to seeing NF paper.
Low Fluorescent, Medium Fluorescent, High Fluorescent and Hibrite Papers
The picture below shows three of these four grades of fluorescence on the top row, with DF, and LF on the bottom row for comparison:
 LF paper gives off an unmistakable light bluish white glow under UV. Generally it can be quite bluish. The stamp at the top left is DF. In this picture, it doesn't look that much duller than the LF stamp at the bottom, and indeed the example here is definitely toward the dull end of the scale. Most LF papers are about mid-way in brightness between the stamp at the bottom and the stamp that is second from left in the top row. MF paper gives off a brighter, lighter bluish white glow. The second stamp fro the left is MF. In addition the stamp shown has the bright Ottawa General Tagging that glows bright greenish yellow. This tagging replaced the Winnipeg tagging and was introduced in 1972. HF Paper is very bright, but less so than the hibrite. The stamp third from left is HF. There will still be a slight hint of blue or violet to the light. Hibrite paper (HB) is unmistakable in the sense that the glow is almost pure, bright white. The stamp on the right is HB. The above picture does not show the differences between DF and LF or HF and HB quite as clearly as I would like, so hopefully the following additional shots will capture the differences better:  In this picture, you can see very clearly that the 8c stamp is much brighter than the right stamp. In addition it has a mottled appearance. That is because the paper is actually DF, but contains a large number of LF fibres that make it appear LF. This is one aspect of paper fluorescence that gives rise to the most confusion because Unitrade has two different ways of describing this paper. On some issues, they call if "speckled fluorescent" (SF) and on others simply "fluorescent" (F). There doesn't seem to be any particular reason for this, but in reality the presence of fluorescent additive fibres should be considered separately from the issue of the ambient fluorescence of the paper because it is possible to have a dead paper that contains a small number of low fluorescent fibres.
 This picture shows the difference between HF and HB more clearly. In practice many of the so called HB stamps listed in Unitrade are really either MF or HF rather than truly HB. The problem is that the issues of definitives have all been studied independently of one another and the descriptions have come about as a result of comparison of one stamp to another. Because fluorescence is relative and a continuum, it really is necessary to study all the issues together and compare stamps across different sets. This is what I have done in listing my stamps. Fluorescent Fibres In The Paper and Naming Convention What complicates the picture is that in addition to the basic grade of the paper, there are often found, fibres which show a different level of fluorescence. These fibres can be very dense, to the point where you can barely see individual fibres, right down to very sparse, where there are only 1 or 2 fibres visible on the stamp. Often these fibres can fool collectors into thinking that a paper is more fluorescent than it actually is, with the above 8c stamp being a good case in point. To deal with this, I have devised a naming convention as follows: (basic fluorescence-fl, fluorescence of the fibres in the paper, concentration of said fibres) So a stamp that had a basic fluorescence of DF, that has a high concentration of low fluorescent fibres would be abbreviated as follows: (DF-fl, LF, HD) For concentrations, I recognize six different levels of concentration as follows: Very, very sparse (VVS) - no more than 1-5 fibres across the whole surface of the stamp. Very sparse (VS) 5-10 fibres across the stamp with no discernable pattern. Sparse (S) a very light sprinkling of fibres across the entire stamp. Gaps where there are no fibres will be quite large - as much as 2-3 mm. Low Density (LD) the entire stamp is covered in fibres, but there areas with no fibres evenly distributed throughout that are up to 1 mm. Medium density (MD) the spaces between the fibres are smaller than 1 mm, but the fact that the fibres are individual is still very clear. High Density (HD) there are so many fibres in the paper that the fluorescence almost appears uniform, but under close inspection it is possible to make out individual fibres. Now it is the case that some stamp papers contain more than one grade of fluorescent fibre. This explains situations where you have two stamps with fibres that appear to have the same overall fluorescence, but look different when you compare them to one another. To name these varieties, I simply add another two sets of initials for the second type for fibre, and more sets for each type of fibre present in the paper. So for example, a DF paper that contains a low density of LF fibres and a sparse concentration of MF fibres would be named as follows: (Df-fl, LF, LD, MF, S) Paper Coatings, Different Readings on Front and Back and Impact on Naming Convention With the advent of chalk coatings that began to be added to papers starting in 1970, the subject of paper fluorescence becomes much more complicated because often the reaction of the front of the stamp will differ from the back. The pictures below illustrate this for the 25c Polar Bears definitive from 1976:   The two blocks shown here are both DF paper. However, one block is pure DF, with a chalk coating that gives the appearance of being dead on the front. The other block has such a high concentration of HF fibres that it appears HF from the back and MF on the front. The naming convention will thus have to be modified to allow the back and the front of the stamp to be differentiated where the reaction on the front differs from the back. This is done by means of a slash. Everything to the left of the slash refers to the front of the stamp or multiple and everything to the right refers to the back. So these two blocks would be named as follows: The left block in the top picture would be: Dead/DF The right block in the same picture is: DF-fl, MF, MD/DF-fl, HF, MD, MF, MD What is interesting here is that the second block actually has two different types of fibres, only one of which can be seen from the front. The reason I know there are two is that on the back the overall density appears to be HD. But then looking at the front there is a lot of space consistent with MD. The reason for this difference is that the MF fibres that are visible from the back are not bright enough to show through the front. If there is only one type of fibre present, then the concentration will either be the same on the front an back, or visible on the back only, but not the front. Finally, there also exists a chalk-surfaced paper during the 1972-1976 period which comes with either a smooth surface, a distinct vertical ribbed surface and a distinct horizontal ribbed surface. The reactions of this paper under UV light are quite varied, but there is a DF paper which shows very clear woodpulp fibres on the back under UV. The descriptions of these stamps will include the word "woodpulp" after the initials describing the paper fluorescence. I recognize that this is very complicated and may appear at first to be to complicated to be workable. However, I believe breaking it down like this will take much of the subjectivity out of the study of paper fluorescence and introduce a bit more objectivity. Anyone have any thoughts about this?
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