Shrinkage – What’s wrong with percentages? Part 2

Just to recap using percentages to calculate how much wool to lay is wrong.

For example:
Jane made a piece of felting that ended up 20cm by 20cm.  Soosie admired it and asked how much did it shrink by?  And like so many other people she said, “Oh about 30%”.

Soosie heads off to her studio to make a similar piece and thinks to herself (obviously its not me cos I would have said it aloud.  To my dogs.) “Mmmmm.    It ended up 20cm, shrank by 30% so 30% of 20 = about 7.  I have to lay 27cm of wool.”

Off she goes felting away. BUT when she is finished the piece is only 18cm x 18cm!?!?!  She made it exactly the same way Jane did – same wool, same layers, same decoration yet it ended up smaller.   WHY?

Because 30% of 27cm is 18cm.  Jane laid 30cm of wool to get 20cm of felt.  You can’t calculate something you don’t know the starting measurement of.  Soosie only knew the finished measurement.  Here in lies the big problem with using percentages.  How do we fix this?  Use shrinkage rates.  Once you have determined the shrinkage rate you can apply it to any finished size to calculate accurately your starting measurement.

And the only way to calculate shrinkage is by making a sample.

  1. Cut a piece of bubble wrap or foam or plastic (something durable) measuring EXACTLY 30cm x 30cm to maske a sample template.
  2. Using the template lay the wool EXACTLY the same way you intend to make the final piece.
  3. Felt the way you usually felt.
  4. Measure the finished piece of felt.  For example 20cm x 20cm.
  5. Calculate how much it shrank by:- Original measurement divided by finished measurement.
    30/20 = 1.5  this is your shrinkage rate.

How do I apply a shrinkage rate?  That’s for the next post.

I will attached a PDf version of these instructions next post so you can print them out.

Keep sampling!  Soosie 🙂

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