Although Unitrade does not list any paper variations for the stamps of this issue, it will become apparent very quickly once you have handled a lot of stamps of this issue that there are indeed some very marked differences in paper, both with respect to colour and with respect to how fine the paper weave is.
Generally speaking, this issue can be found with paper that shows either:
1. Very clear mesh on the back that is coarse.
2. Mesh that is not as clear as above, but is still visible when the stamp is viewed face down on a surface.
3. Paper that shows no clear mesh pattern unless the stamp is held up to a strong light source, when the mesh becomes visible.
Each of these types is found on most all values of the set.
In addition to these variations in weave, there is also variation in colour:
1. The predominant paper type is white vertical wove. In theory, horizontal wove may also exist, since the 5c can be found on horizontal wove paper. However, I have not seen any white paper stamps of any value on horizontal wove paper.
2. Some printings of the 1c are found on a greyish wove paper, similar to a greyish wove on which the first printings of the subsequent 1c Admiral issue are found. Logically, it would seem that these are from the last printings made just before the Admiral issue replaced this one. This would seem to be supported by the fact that most of the 1c stamps I have seen on this paper are printed in shades of blue green, which is the shade group most commonly associated with the last printings of this value.
3. On some printings of the 1c, 2c and 7c made between about 1905 and 1907, there was a toned paper used. I have considered the possibility that this is simply white paper that has been affected by age or by reaction with the gum. However, I am inclined not to believe that this is the case after seeing several postcards in pristine, fresh condition with stamps affixed that are on this toned paper. To me this is significant because the gum in this case has already been moistened, activated, bonded and dried over 100 years ago, so it does not seem that it would continue to react with the paper significantly. Secondly, I have seen many used examples that show the toned paper colour, even though they were soaked and the gum removed decades ago. My dates above are pure conjecture and based simply on the postmark dates I have seen on the used stamps I have encountered on this paper.
4. The 5c value is the only value found on bluish paper. The blue colour varies from a very light blue, to light blue, to greyish blue to greenish blue. The very lightest of these blues is almost white and it is what Unitrade refers to as the "whiter paper".
The toned and greyish papers are generally found with either coarse or fine vertical mesh showing through on the back and mint stamps generally will have either cream coloured gum with a satin sheen, or yellowish shiny gum. The gum on the bluish paper stamps is generally always yellowish and this is apparent from the fact that the paper colour of mint stamps appears greenish from the back, rather than blue.
For the white paper with no visible mesh, the gum is a smooth cream that has the appearance of being "sponged on", as it has a satin, semi-gloss sheen, rather than being shiny. We see this type of gum on the previous Numeral issue, and we will encounter it again on the post World War 1 wet printings of the Admiral Issue stamps.
I will now illustrate some examples of the above variations on each value. The gum on all stamps shown is 100% original and shows that there is considerable variation in the appearance of the gum on this issue.
The One Cent
If you look carefully at the stamp at the left in the above scan you can just make out a very fine vertical mesh pattern, but it is by no means obvious. This is what I am referring to when I speak of fine vertical mesh. The pair in the centre and the stamp at the right show the coarse vertical mesh, which should be very clearly visible when the stamp is placed face down on a surface.
The above scan shows some of the gums that can be found on this value. The first two stamps in the top row, the right stamp in the top row, and the bottom left stamp are all on the coarse mesh paper, and in each case the gum is either a yellowish shiny gum (bottom left and upper right stamps), or is a yellowish satin gum. The third stamp on the top row and the second stamp from the left on the bottom are on paper showing no clear mesh. In both cases it is the "sponged on"cream gum described above. The third stamp from the left on the bottom row is the greyish paper, with coarse mesh and it has shiny yellowish cream gum. Finally, the lower right stamp is the toned paper showing fine mesh. In this case the gum is clearly a creamy colour and is not really shiny, being more satin in sheen.
The Two Cent
It is difficult to see in the above scan, but the stamp at left has coarse mesh and the second stamp from the left has fine vertical mesh. The two stamps at the right have no clear mesh unless held up to a strong light source. The gum on the first two stamps is shiny yellowish cream. The gum on the third stamp is the "sponged on" cream gum described above, and the right stamp has cream satin gum, as the lower right stamp on the 1c above.
The Five Cent
The top right and centre & right stamps at the bottom are on blue paper, while the upper left and upper centre stamps are on greenish blue paper. Finally, the lower left stamp is on pale greenish blue paper, commonly known as the "whiter paper".
As you can see from the above scan, the gum is always yellowish. On early printings it is smooth in texture, but on later printings it is streaky, as shown on the second stamp from the right.
The above scan shows the greyish blue and greenish blue papers. The greyish blue is shown at the left, and there is no visible vertical mesh. The greenish blue is shown at the right and the example here has the fine vertical mesh.
The Seven Cent
The scan above shows the gum on several mint stamos and the smooth no-mesh paper on the used stamp second from left. The fourth stamp from the left is on the toned paper and has the cream satin gum described above on the 1c and 2c. The others are mostly the fine mesh papers with yellowish cream shiny gum. The stamp at right has no clear mesh and the "sponged on" cream gum described above.
The left stamp has the fine mesh, as does the centre stamp on toned paper. The stamp on the right has the coarse mesh.
The Ten Cent
The above scan shows a used deep greyish olive green on white paper with the coarse vertical mesh.
Unfortunately I now only have one example of the 50c value. The above stamp is the deep bright purple on soft wove paper with fine mesh and has the shiny yellowish cream gum.
Hopefully after reading this post and looking at the scans you will agree that there are definite differences in the paper and gum that are significant because they follow distinct patterns across the values of the set. I would be interested to hear your comments and thoughts on this topic. Do you think these differences are collectible? Or am I going overboard here?