Australia #576 1973-1981 Definitive Issue, Two VFNH Examples of the $4, Each on a Slightly Different Paper
Two VFNH examples of the $4 "shearing rams" stamp from the 1973-1981 definitive set, both with PVA gum and printed on low and medium fluorescent papers.
The Australian equivalent of tagging is called Helecon, which is a chemical in the zinc sulphide group that fluoresces orange-red under long-wave UV light. The very first stamp to be issued with Helecon coating applied to the paper was the 11d Rabbit Bandicoot from the 1958-1964 definitive issue. Later, the 5d orange-red Queen Elizabeth II stamp from the 1963-1966 issue was issued with the Helecon incorporated into the ink. By the end of 1965 all stamps issued had Helecon applied to the paper. On this issue, some stamps are found with a uniform coating on the paper that glows orange-red, while others have the paper impregnated with Helecon, so that it appears greyish white from a distance under UV, but under magnification, tiny orange-red dots can be seen on the surface of the paper. Most of the chalk-surfaced paper stamps from these issues are like this.
The paper fluorescence also varies from medium fluorescent to hibrite. Again, you can see these differences from the picture showing the back of the low value gemstone stamps under UV light.
The gum is generally a dextrine gum that varies in its sheen, from a crackly satin gum, to a shinier gum. Some of the later printings of these stamps have PVA gum, which also varies in its sheen and overall appearance.
Scott lists the basic stamps at $10.50 for VFNH. The stamps here grade 80.