We did some research on the internet and used a vinegar mordant. This was the colour of the wool in the beetroot juice:
We had read that beetroot actually resulted in a muted colour, and this was our final result:
Its a rather nice pale pinkish fawn colour. However, since the boys wanted me to knit socks from this wool, I think we will overdye it with something else. It was fun to try a natural dye like this and a good experiment for Finlay and I.