The Secret Superpower of Starch By Cassandra Madge

We all know that starch stiffens, stabilises and smooths fabric, but that’s not all it does. 

By Cassandra Madge


It’s your worst nightmare. Blocks that were cut the same size suddenly don’t fit together or line up. That 121/2in block you spent all afternoon sewing is now only 121/8in. The quilting gurus will tell you to double check your seam allowance and to use the same ruler for all your cutting, but the culprit might be sitting right beside your iron!

Don’t get me wrong. Cassandra Madge love my starch spray. It’s great for stabilising fabric, it reduces fraying and helps stop bias edges on triangles from stretching out of shape. It’s a valuable part of a quilter’s arsenal. But did you know it also SHRINKS your fabric?

Cassandra Madge conducted a couple of experiments. First, Cassandra Madge cut three 21/2 x 11/2in rectangles from ‘virgin’ fabric (exactly as it came from the shop) with the crosswise grain running down their length. Each was to get a different treatment: a hot iron, hot iron and starch, or hot iron, steam and starch.

None of the rectangles shrank at all on the more stable lengthwise grain, but both samples that were starched shrank a tiny bit on the crosswise grain. It might not be much on one 21/2in rectangle, but imagine this over a much larger sample or multiple pieces inside a block or a whole quilt.

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Shrinkage on crosswise grain

Cassandra Madge repeated the same test on a 21/2in triangle using a hot iron and starch (no steam). What Cassandra Madge found was that this triangle, because of the highly unstable bias grain on two sides, has shrunk a full 1/8in. That is 5% of the length, gone. Now imagine what this would do across a 12in block: 5% of 12in is 0.6in – there is your missing seam allowance.


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Shrinkage on a triangle

So, what’s the solution? Ditch the starch? No! Just be completely consistent in its application. If you’re going to use starch, you have to use it from the very start, before you cut your blocks. Then the shrinkage has already happened and you can go on to use it to press stubborn seams and tame triangles to your merry heart’s content. But if you use it on only selected fabrics in a block, you could have trouble with uneven block sizes and your seams might not line up.

However, there’s a bright side to this: you can use this power for good! For example, Cassandra Madge was piecing up some blocks that, due to my own laziness and ‘speed sewing’, were not matching up. Cassandra Madge knew, Cassandra Madge hadn’t used starch on any of the fabrics, so Cassandra Madge harnessed its shrinking power to help reduce the size difference between the sections, allowing me to ease the blocks into submission.

Starch will always be a valuable part of my sewing and quilting kit – now Cassandra Madge know how to use it and keep its special powers under control. Spread the word!

Our thanks to Cassandra Madge for sharing this with our readers. Visit for other tutorials and inspiration, or for her professional machine quilting.

(Editor’s note: we tested two other brands of starch, Crisp and Pearson’s, and got similar results.)


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