Prewash or not: two fat quarters of deep red
I had never prewashed quilting fabric until this winter, mainly because I like the way an unwashed top crinkles after its first wash with the batting. Then I bought two fat quarters of a deep saturated red for a star block and had a feeling about them. I cut a two inch square from each, dropped them into a glass of warm water with a square of white muslin, and left them for half an hour. One square did nothing. The other turned the water the color of weak tea and left a pink shadow on the muslin.
That settled it for the reds, and it made me curious about shrinkage, which I had always treated as a rumor. I measured both fat quarters before washing, 18 by 21 1/2 inches, and washed them in warm water on a short cycle with one of those dye-catching sheets, which came out streaked pink. After a tumble dry on low and a press, the bleeder measured 17 3/8 by 21 1/8. That is roughly three percent along the lengthwise grain and almost two percent across. The other fat quarter lost about a quarter inch each way. If those two had gone into one block unwashed, the block would have pulled itself out of square at the first wash.
Prewashed fabric is softer and more unruly to cut, so I now press each piece with spray starch after drying, which brings back enough body to cut accurately. Precuts, the small five inch squares and the 2 1/2 inch strips, I still do not wash, because the fraying would eat into the seam allowance and the pieces are too small to measure sensibly anyway. I accept that quilts made from them will be slightly less predictable.
So the rule in this house is now: prewash all yardage and all solids in saturated colors, test anything red, purple or very dark with a swatch in a glass of water, and leave precuts alone. I also keep a dye-catching sheet in the first wash of every finished quilt no matter what went into it. The red star block, for what it is worth, has been washed twice and the cream points around it are still cream.