For this project, I have used a previously blocked hat and covered it in both new and vintage fabric for a sustainable mix of methods.
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Pull the fabric on the right side over the foundation base. Ensure that you have a seam allowance over the bottom edge of the base. Double backstitch the edge of the fabric to the bottom seam allowance of the foundation base.
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Create a tube of fabric that is twice the height of the foundation shape and features a bias seam join at the back.
Run a gathering stitch to hold the pleats together at the top.
Fold the top of the fabric towards the inside of the foundation base so the fabric has a hem. Divide the fabric into four segments on the NSEW points. With each segment of fabric, fold small even pleats that all face the same direction.