Hold on a mo here.
The smaller steel tanks often found on late model 40's and some of the century type motors in the 1970's appear to be powder coated. Black or blue seem to be the 2 normal colours here, and larger "long range" tanks (generally) are painted. Some "long range" tanks came in brass as well, just like the steel variants.Decals are slightly different too with many of these "ugly" tanks. Rust usually gets the better of these tanks in the long run, and very often get swapped out with an older oval brass tank.
From what i've seen to date, 9 out of 10 tanks made before the 70's are generally brass and painted,and so far most of the tanks i've viewed have had very little in the way of remaining paint or decals on them. Once in a while you'll come across that "mint condition" tank that's been hidden away for years. I bet many of them were painted with a proprietary brand of shiny clear coat to protect the decal. Anything from the 70's to early 80's tends to be a powder coated steel affair, usually blue or black with corresponding decals. 80's onwards for most appear to be plastic and generally a "long range" similar in size to the older steel ones. Aside from the wartime and pre-war models, i think that about does it.
So, the question remains. Shiny or dull finish? Lacquered or varnished? or something other...?
For me anyway, following as best as i can see in older photographs, quite a lot appear to have a fair shine in the pics which leads me to believe there must have been some sort of clear coat over the decal and paint. It's risky i know to put all my eggs in one basket like this, but thinking rationally for a moment, photoshopping didn't exist from the humble beginnings of British Seagull, but photography certainly did. We've talked before about how BS often used the same generic sets of photo's for their advertising unless there was a very real need to change things. Pictures,and we're talking about black&white here, no matter how grainy they can appear at times provide a tantalising glimpse into the past. Look a little bit closer and you'll see what i can. Shiny paint is often an indication of a varnish or lacquer coat, a dull finish might perhaps indicate a less fussy finish. A lot of these older gulls may not have all their correct clothes about them any more, but look a little closer and you'll find clues here and there. Underneath fuel tank straps on older 102's and around the tank mounting bolts/studs are 2 of the more obvious places to look.
A paint depth gauge would soon put this to rights. I might just be able to put my hands on one for a better assessment.