Believe it or not, elasticated panels were used in some stays in the Regency period. The stretch was achieved by metal coils - no elastic in the eighteenth century! I am fascinated by one particular exhibit at the Kyoto Costume Institute in Japan that was featured in an exhibition in 1989 called Revolution in Fashion 1715-1815 Revolution in Fashion 1715-1815 (kci.or.jp) For copyright reasons I'm not allowed to show it here but it is from the transitional period so isrelatively short and features cording, whalebone and a stretchy side panel toeards the diamond shaped back panel. It is on my list of designs to make. Over the weekend though I made this one;
Which was based on this example from the Metroplitan Museum in New York
I used shirring to achieve the elasticated section under the cup which is a technique I have never done before and now I'm hooked. I've always been a secret fan of smocking! It's so easy to do - all you need to do is hand-wind the bobbin with elasticated thread - you need to make sure your panel is larger to accommodate the shrinkage of course.