I am currently starting the dissertation process and I need to think of a possible topic. I am interested in modern history (specifically the 20th century). I also love cosmetics and I am currently looking at a dissertation topic which researches the role of red lipstick in WWII in the US. I would look at pin-up girls, how red lipstick increased morale, how red lipstick strengthened working women, patriotic advertising campaigns and magazines. Do you think this sounds like a plausible idea with enough historical discussion to please the markers?
I think it would be a bit hard, if only because it is so specific and quality academic histories on makeup as a subset of fashion are vanishingly thin on the ground, at least last time I did a personal interest lit review in that zone, which was about a year or two ago. I do believe I have seen this topic covered in the pop history stuff as well, so you need to find a way to go deeper. You might be able to pull in some of the recent economic/social research on women's consumption of makeup increasing during the recent recession, for like, a grand universal theory of strife-makeup I suppose? Have you done a lit review yet?
I am not as versed in fashion history as some ( cough all-mighty moderator /u/chocolatepot cough), but it strikes me that red lipstick might be a chapter at best for a diss. The source base might be enough to sustain a chapter (ca. 30-70 pages), but stretching it out for a full dissertation might be a hard task (of course, the sources might prove me wrong on this- that's why it's called research, if we knew for 100% certainty, there would be no point to a dissertation!). If you're at the start of your project, you'll probably want to look at the broader historiography of both makeup and consumption and how they intersect with other topics such as gender images during wartime, the domestic chemical industry in the war, or rationing of consumer products. As /u/caffarelli points out, sociological research on makeup will also be your friend as is the voluminous historiography on consumption. Even if you do not ending up using this scholarship in the dissertation, it will help you in writing your prospectus and defending it to your committee because you can frame WWII lipstick and/or makeup into other fields of research or disciplines.
You should probably think about which kind of sources are available for testing your thesis.
I mean there are probably a lot when it comes to pin-ups in general, but if you narrow it down to red lipstick specifically you may find yourself short, especially for testing such grand narratives about morale and strengthening working women etc.