Stamps Catalog - Wavy line permanent, Denmark

There aren’t too many countries that can boast definitive sets that have run for over a century, but Denmark can. Its ‘Wavy Lines’ series was first issued in 1905, and is still going strong today!
The design, by Julius Terchilsen, includes symbols from the Danish Coat of Arms, along with three waves intended to represent the three straits that connect the North Sea and the Baltic Sea: the Storebælt (Great Belt), Lillebælt (Little Belt) and Øresund.
There are three essential groups of these iconic stamps to collect.
From 1905 to 1933, the stamps were printed in typography by H H Thiele, which had printed all Danish stamps up to then. They are distingished from later issues by having nine hearts incorporated in the design.
The first printings, ranging from 1 øre to 12 øre in value, were on paper with a Crown watermark, but later ones had a watermark of Multiple Crosses. The change of paper came with a change in perforation.