->I still have a problem to understand paint technology of that time
(19-turn of the 20th cc).  I am working with existing paint layers (both
interior and exterior surfaces) and can not explain some of features of
them. >

Igor, please be specific.  What features of the existing paint layers are
puzzling?

I found another interesting 1919 passage:

"Painting Russia Iron
The best method of painting Russian iron depends on whether you desire a
flat or a gloss finish.  Oil paint is apt to crawl or creep on that polished
surface and it is best to use pigments ground in japan.  For a flat finish,
thin the color with turpentine and add a trifle of rubbing varnish, say
about one tablespoon to one pint of the thinned material.  This will keep
the flat color from cracking and scaling.  It is best to first give the iron
a wash with benzine to remove any grease, because even the perspiration from
hands on such surface is liable to throw off the paint.  For a gloss finish
you can either varnish the flat coat or coats or you can reduce the color
ground in japan with a suitable varnish and put this over the iron direct or
over one coat of flat paint, the latter course being best, if not too
expensive.  When the iron is to be subjected to heat, as in the case of
heater pipes, and black is not objectionable, high-grade turpentine
asphaltum varnish will serve the purpose, but it is ill-advised economy to
use a cheap grade containing coal tar, rosin and benzine, such a nostrum
perishing in a short time."

John Mascaro