This is an essay written by the artist Emil Carlsen and published in 1908.  I'm not entirely sure of the source, but it may be a magazine called Palette and Bench.
Note:  In the essay Emil Carlsen recommends the use of zinc white.  Based on our understanding now, we know that zinc white is not archival and becomes very brittle over time.  Current expert suggestions would be to never use zinc white.  Lead and titanium would be good replacements.