Making tinctures

[Carrie]

I'm writing a course on growing and using herbs and am wondering exactly how other folk make tinctures. I always thought you just soaked herbs in vodka. But my Penny Ody book says that you mix water and vodka to get a mix that is 25% alcohol. So if you start with vodka at 37.5% alcohol, you add 500ml of water to every litre of vodka to get a 25% mixture.
I don't suppose it's critical as either way will get the important ingredients out of the herb and into the liquid - just that Penny's method will be less alcoholic which is probably a good thing - unless you have a really bad cold!
How do you make a tincture?

Carrie