I just can't help but chime in here on this subject.............
If one is building a desk top, no weathering, like new crisp paint, then it is Ok for the shinny bling bling. Thats were that got its start and many years ago, Japanese mfg's would include brass props w/their motorized kits. Now I will say this, I like the fact the prop is brass, if only they would make from bronze.
Now, as stated, bronze is a better color to paint, but how I get to that is this way.......I spray with Alclad Gloss Black........once completely dry, Alclad II copper. Then after dry, sealed. Time to get the bronze effect. As has already been pointed out, a wash or thinned brown is applied to the prop, this results in a nice bronze brown metallic look. Now that prop needs to be weathered just a tad, so just like the copper sheeting on a hull turns green, so does the salt that collects in the creases of the prop blades where they attach to the boss. key word suttle, suttle effect with a light green/white mix wash. Let dry and seal again w/a semi-gloss finish.
Plastic or metal, this can be done to great effect and makes the ship pop with realisitic looking props.
Now, there are brass props on small boats and one has the option to take a real brass prop, drop into a glass of water mixed with salt and then remove the prop after you see the effect you are looking for. Rinse w/clean water, dry and seal. You get a very cool effect on a real brass prop.
Or again, mount them after a good polishing for that bling bling effect. It really is up to you what you want.
I have a Mobus Skipjack and yes, I sprung for the $30.00 brass prop and will shine it nice and shinny to install on my Admirals Display of the Skipjack...........
Just my worth..........Rick from NC