Above shows two styles of Victorian corset, the black adapted slightly, & a costume I designed & built (the character was a time traveling Lady assassin!) for a short film in 2010, illustrating the great effects a corset can have when working with period clothing.
I’ve just found the most useful link to questions & answers about plastic versus steel boning when making historically accurate corsets or stays.
Acacia’s comment nearer to the bottom agrees with my own techniques when tackling this problem. As I don’t often have the money in a films budget to use all steel I too mix plastic, spiral & steel where necessary however; it is interesting to read how others have been tackling this issue.
Rigilene- or fabric store bought boning- is of no use to us as it is far too light weight. I feel faint whenever I hear an assistant in my local fabric store recommending it & on more than one occasion I have tried to slip them a website for the correct boning!
There are some very good whalebone replicas out there however; if you want to make a corset 1800 or later steel should very nicely suit your needs, mixing it with plastic will make it more comfortable & slightly cheaper.
I have also remembered a couple other websites for corset supplies:
Bra-Makers Supply: http://126.96.36.199/site2009/cart/shopdisplaycategories.asp
McCulloch & Wallis: http://www.macculloch-wallis.co.uk/Default.aspx
Laughing Moon Mercantile: http://www.lafnmoon.com/ who sell a great range of historic corset patterns.