How to Identify the Classic Finland Serpentine Roulette Stamps (Sc#4-13)

The early classic stamps of Finland (Sc#4-13: 1860-1874) can be difficult to identify at first, but once you know what to look for, it’s relatively simple.
Scott defines four types for these stamps (Type I, II, III & IV). The significant differences can be easily spotted in the depth of the perforations and the shape. Type IV is difficult to find and much more valuable, but easily identified by it’s shovel shaped perforations.
Use the following images to help you identify these classic stamps from Finland.