Kai used three nice stamps on the envelope:
The stamp at the right side was issued to commemorate the fact that Porsgrunn was granted limited city status in 1807, which was expanded to full city status in 1842.
This stamp was voted the most beautiful Norway stamp issued in 2007, and I can only agree that this is a very beautiful stamp, just the kind of stamp I like! :)
The appearance of a ship and a vase on the stamp show the importance of the shipping industry and the china factory in Porsgrunn.
The Norway post website tells you the complete story, so for those of you who are interested: go check this website! :) (http://www.posten.no/Portal/English/NorwayPostPhilatelicServices/Read+more+1644.htm)
The other two stamps show butterflies, and were issued in 1993. The first one is the Orange Tip (Anthocharis cardamines); and the second one is the Small Tortoiseshell (Aglais urticae).
Tomorrow I'll be back with another cover. I don't know which one I will show tomorrow, but it will be a cover from one of these countries: China, Switzerland, Australia, Poland, Luxembourg or Republic of China (Taiwan) because these are the countries I received an envelope from last week.