Off the top of my head, I'd add Smalandshyttan (photo attached), Strombergshyttan (Gunnar Nylund), Johansfors (Bengt Orup), and iitala (Errki Vesanto). I confess that I tell by only buying ones that are signed or have labels. Often, the non Landberg have a brown in them (Smalandshyttan, Strombergshyttan, and Johansfors, for example), whereas the Landberg seems alone in having a deep charcoal).
The number on Ivo's piece seems anomalous in that it has five numbers, whereas all five pieces of similar Landberg of mine have only four. I referred to Ruding's chapter in the Orrefors book, but that didn't take me further. They started using five numbers in 1980 but it seems the first 2 numbers were 90.
That leads me to what might be another thread, "When is a charcoal sommerso piece by Nils Landberg correctly called "Dusk?" Friedman identifies three pieces as Dusk on p. 93 of his book, the numbers are 3538/5, 3596/1 and 3558/10. Duncan on p.126 of his book shows very similar pieces but calls them "Group of heavy-walled pieces,...1955-57."
I've taken a quick and dirty picture of the pieces I have. They're all marked "Orrefors NU", except the one on the extreme left which is marked "Orrefors or." The numbers are (from the left), 3538/138, 3812(the 2 here is a guess), 3538/5, 3736, 3857/8. Which pieces would qualify as "Dusk?"
Anyone know who started the style, or is the style more a representation of a then prevailing sensibility?
I forgot to add what jealousy a phrase like "bought that in Stockholm the other day" can create in someone in far off Vancouver, B.C.