They are often called tea dresses today, but it is not a period term - there were 'tea gowns' at the time, but those were floaty 'at home' kinds of things with artsy flowing sleeves etc; these types of white cotton lace insert dresses were intended for summer outdoors wear for a variety of events. If you look at old photographs you often see women wearing them to fairs, weddings, summer promenades and on holiday at places like Atlantic City... They are always made of cotton, usually a thin weave like a lawn or batiste but I have also seen them in cotton crepe. The crocheted buttons were more 'artsy' than shell buttons at the time, but I don't think they were more expensive or desirable - just a different taste. I have seen that type of heavy woven lace before but I am not sure what it is called...