Genuine
Forgery
This test does not guarantee genuineness,
but it weeds out forgeries of the 8t passed off as 4t.
Look here for more details.
Click image for plain view
Bibliography
The Work of Jean De Sperati by the British Philatelic Association 1955
Album Weeds by Rev. R. B. Earee
The Serrane Guide by Fernand Serrane
The Forged Stamps of all Countries by J. Dorn