Another great reason to buy vintage!
If I am going to sew a dress (a rare occurrence these days!), I always pre-wash the fabric, just to make sure it's pre-shrunk. When you buy a new (non-thrifted or non-vintage) dress (or shirt or jeans), it's not always the way, and things do often shrink in the wash. Why? They haven't been pre-shrunk of course! Mechanical shrinking (also known as sanforizing ) is a process whereby the fabric is forced to shrink width and/or lengthwise, creating a fabric in which is basically preshrunk. Sanforizing was patented in the USA in 1930 by - wait for it - Sanford Lockwood Cluett. Chuett eventually joined the family firm of detachable collar manufacturers, but he was also an inventor with around 200 patents in his name.
It appears that anti-shrink fabrics, both cottons and rayons, first arrived in Australia in 1939, judging from the ads I have found in various editions of the Australian Women's Weekly. The ads also seem to disappear by the late 1950s.
How does it work? Basically the cloth is fed into the sanforizing machine which steams and presses it with a rotating cylinder, and the cloth is laterally expanded and then relaxed against a rubber sleeve that does the same thing - it gets shrunk. The greater the pressure applied to the rubber sleeve, the less the shrinking afterwards.
So now you have cloth which does not shrink significantly during clothes production or by washing the finished clothes. Obviously this process makes the fabric more expensive, so cheap fabrics used in cheap products, like those you buy at chain stores, will not usually be pre-shrunk.
Just another great reason to buy vintage or preloved clothing!