Henre,
I'll answer your question about brushing here quickly (from what I've read in the book so far) and follow up with more detailed information when I can put together a detailed summary.

The book in question (Automobile Painting, published in 1919) first talks about the most common finishes on cars of the day. Apparently, the tried and true method of the time was a "rough coat" and/or "color coat" (actual terms from the book). This was a lead based pigment / paint which provided color, but not gloss. After the color coat was applied, then a varnish coat(s) were applied. Interestingly, this was the early 1900's version of Base Coat / Clear Coat (I guess everything new is old...). When they speak of the action of painting they are referring to laying down this type of color coat (without gloss). The technique for brushing paint is to use as little paint as possible and spread it as thin as possible.

When they get to the Varnish (clear coat) stage, they say that the technique for brushing this is different. (This is important because later they discuss ENAMEL -- which is what Rustoleum is -- and they say that Enamel for color is the same in technique as applying the clear varnish). They say that you want to put on a lot more material and "flow" it for varnish and enamel, brushing in single directions from the starting point on the panel, and then "tipping" in one cross direction then the other to help it self-level. Do this quickly and then leave it the hell alone. Tipping should not cause the brush to drag or bind in the varnish / enamel at all. If so, you have overworked the material or have waited to long to come back for tipping. They reference the fact that after the varnish / enamel is flowed up and tipped, brush strokes will still be visible, but that they should be left alone because they will self level.

Most of the description of technique is for varnish -- but the final chapter discusses enamel paint (at the time it was the modern, production material for painting -- but was typically done with spraying and baking). The chapter basically says 1) enamel is color and "varnish" as one and 2) follow all the techniques for varnish for application. They suggest that a car may only need 2 coats when brushing (not rollering!) enamel because the coats are fairly thick. They recommend thinning the first coat of enamel (30% -- with turpentine -- but I think we all know to use mineral spirits). Let dry 48 hours. Wet sand, then apply the final enamel coat without thinning. They seem to suggest that after the final coat no more sanding / polishing is required.

For runs in enamel / vanish they say to attack immediately and try to flow out with the brush. If brush drags, then a smaller brush with some additional enamel / varnish to help dissolve the local run / sag then flow out with brush into surrounding area. For a more stubborn or more dried run/sag, often times a "heating iron" held close to the surface (but not touching) the panel will cause the run to flow out on its own.

Proper brushes for enamel / varnish:
(I'm sure these are out-dated terms, but with a little thought we can probably translate to the modern day).
One basic style, but two different bristle varieties.
-- In my picture in the previous post, the type of brush for enamel / varnish is Figure 4 -- which is the bottom most brush in the diagram. ---
1)"Extra Fitch Hair Flowing Brush, Double Thick" also known as "Badger Hair Flowing Brush, Double Thick". Has long handle and fairly short bristles. Best ones have the bristles set in rubber. According to the book "Once these are broken in, they are a joy to work with".

2)Same style and shape as #1, but bristles are made of "selected Chinese Bristles" or "finest French White Bristles". They say that this type of brush is stiffer than #1 (requiring more effort in application) and it has longer and thicker bristles. This means it carries more enamel / varnish. Because of carrying more enamel / varnish -- it lays down faster and causes better flowing and self-leveling.

Hope this helps.

-- Dan