The following instructions are lifted from the New Lanark website and applies to most of my work:
"Pure wool should be washed gently by hand in pleasantly warm water. It should be rinsed in water of a similar temperature and gently squeezed dry. Hot water, significant changes in water temperature, rough handling and leaving to stand in water will make pure wool fabric felt. Machine-washing can also cause shrinkage, however a ‘hand rinse’ or ‘short spin’ cycle in the washing machine may well be successful for pure woollens. If in doubt it is best to test a sample of knitting first."
Where items are hand washable only, I recommend using a detergent designed specifically for woollens such as Dreft or Stergene.
Items made of acrylic may safely be machine washed at 40 degrees Centigrade.
I have sold a few items made with pink yarn which is 20% wool and 80% acrylic. Unless otherwise stated on the price tag, this yarn can be machine washed at 40 degrees Centigrade using the wool cycle. Where the washing instructions differ, it is because the item has a button that is only suitable for hand washing.
My few cotton items are best hand washed. Although cotton yarn is usually machine washable, the ball bands on the varieties I used advised against it.