>>looking for the architectural manuals 19-turn of the 20th c. with
recommendations how to prepare for painting and paint the surface of
cast iron.>>

From "1995 Paint Questions Answered" - The Painters' Magazine, 1919:

"Mixing Dry Red Lead with Linseed Oil for Painting Iron Structures

A great deal depends on the purity and fineness of the dry red lead, but
we should say that 25 pounds or pure, dry red lead should be thinned with
one gallon of pure raw linseed oil, by stirring the oil in gradually, and
should
the mixture become lumpy it should be strained through a piece of wire
cloth or paint strainer.  This will make one and half gallons of stout paint,
which, when brushed well in to the iron structure, will not run.  If the
job is to be hurried, a gill of good oil drier or turpentine japan may be
added
to the mixture.  If the iron be fairly smooth and plenty of elbow grease
used, such paint will cover 700 square feel one coat to the gallon"

It is intriguing that, although factory-mixed paint was available, all
recommendations from this book (composed of published contractor magazine
questions and answers) explain how to mix the paint from scratch.  It seems
that, even in 1919, painters (probably, at least, the best of them) still
were quite verse in the properties of the components and mixed their own
coatings!   Hope this was of interest.

John Mascaro