It was purely for appearance! The decison could be made by either the owner, the captain or the chief mate. Some ships painted their yardarms white as well. By yardarms, I mean the extremities of the yards ( the last foot). The yards go across the masts and support the square sails. These are often referred to incorrectly as "yardarms!" Other ships, especially British ships of the iron & steel variety often had black yards. White lower masts and doublings were popular into the early 20th century. Same with painted ports. They didn't open, they were just painted on!

Here is a picture of my little iron-hulled Phasis with white lower masts and doublings.

Bob

Edited By Bob Wilson on 12/02/2013 19:43:20

Edited By Bob Wilson on 12/02/2013 19:44:31

Gareth,

They were, as you say, to carry extra sails sticking out from the sides, but they were not yardarms. Their correct title was "studding sail booms." But they were always referred to as "stunsail booms" by seamen, probably because it was easier to say. They shortened a lot of words such as topgallants became t'gallants or even just 'gans'ls. Forecastle became fo'csle and boatswain became bosun.

Bob

I understand that the white paint was originally applied to points where the different sections of the mast were connected. It was at these points where stress loads were the greatest and there was a higher risk of failure, the white paint made it easier to see any splits in the timbers from deck level.