Boker did not have the best etching process. The etching results usually had a rough appearance. Therefore, Boker used a very dark, blackish substance on the etches to "hide" the etch imperfections. To my knowledge, it is the only manufacturer to have done this. Others used the gray coating or no coating at all.
You might be right Grumpy,
but the 3rd close up,shown in my post,is from an 121.
Gerd
