I was interested to see how the dress is finished on the insides. The period is too early for overlocking, and besides the overlocking stitch is quite heavy with the threads, and I believe that it might be seen as a ridge from outside of the dress; the same issue would be present with French seams.
My research, both in books (See Arnold, 1966, p.83) and at the museums at Bath and Blandford gave me two options: to leave the edges raw, or to overcast the raw edges of the seam allowances by hand.
I was surprised to see so many of the 1930s dresses left unfinished on the insides, with raw edges; however, larger seam allowances were often given (around half an inch) and additionally, the fabric of that period was definitely of better quality, with a higher thread count, when compared with similar fabrics available in today's market. Therefore, the fabric had actually survived intact, and the dress was neither damaged nor any worse for wear, by leaving the edges raw. On a chiffon dress, the seam allowances were trimmed (or perhaps had frayed?) to as little as 1/4"; but the seam had still not deteriorated.
On other dresses, the seams had been overcast by a whip stitch done by hand, which was quite inconspicuous and a little more protective of the seam allowances.
An option for me would be to carefully zig-zag machine stitch down the raw edges, placing the stitch over the raw edge so that the thread draws the edge in close - as I would finish raw edges of the cloth on a pair of tailored trousers. This would be much quicker, however I didn't want to risk the machine catching or pulling on the fine crepe cloth, or there being a discrepancy with the top- and backing fabric (i.e. if one of them slipped under the foot).
Although I am not aiming to accurately reproduce a 1930s dress (as my classmates are for the Patterns of Fashion competition), I do want the dress to have a feel of authenticity which reflects my research into this period. I therefore decided to do the historically-accurate finishing by whipstitching by hand.