In the 19th and early 20th c., house painters would very often be mixing their own paints, buying barrels of red iron oxide , white lead, Prussian Blue, etc. ( sometimes dry, sometimes pre-mixed in linseed but very thick ) then stirring them ( or mixing them in a small ball mill) with linseed oil, along with some Japan drier to make the paint set up faster. They would very often first put down a primer coat of yellow ochre ( also an iron oxide) that would make the underlying color of the wood or masonry more uniform, and seal the surface. The ochre was usually cheaper than the pigments in the top coats, so it saved some expense. Several coats were expected, for protection and uniformity. But painters had to do more than simply brush from a bucket- they were usually stirring to keep the pigments from settling in the bottom, and depending on the job would vary what they were applying, working with boiled linseed, raw linseed, adding turpentine ( "turps") for thinning, varnishes for increasing the body, rubbing down the new paint with a rag or some tow to smooth out the roughness of the lumps of pigment.... For a brick wall, for example,

Prime brick work with a thin coat of good paint mixed in pure linseed oil. Flow on the priming freely, and brush it well into the brick; for second coat, whatever paint you use, put in at least one-fourth white lead; make this coat one-third turps, and rub it well out. Give it a good body. For the last coat, use your color regardless of lead, unless you want it in to get your color. If you want a gloss, mix this coat with all boiled oil, and flow on. For flat, if your colors are ground in oil, use one-fourth oil and three-fourths turps, and if it don’t show flat when painted, it will flat in a short time. The last coat may admit of more oil or may not take as much, and flat. This depends upon the work when started, etc. Some painters make brick flating by breaking up the pigment in japan [a hard rosin varnish], and elastic varnish for a binder, and thin with turps. I prefer the oil for a binder, and have made the last coat one-half oil, and had a nice flat in a few weeks. I always ridicule the idea of painting brick flat, because it will not stand as long as an oil finish, and the oil finish will be flat enough in a few months.

White, W.F. (1919) The Practical House, Wagon and Automobile Painter. Shrewsbury Publishing Co. https://www.gutenberg.org/files/67109/67109-h/67109-h.htm