Pressing is the half of piecing nobody films. You sew a seam in twelve seconds, then spend a minute at the iron, and that minute decides whether the block lies flat or rocks on the table. Most blocks that finish the wrong size were pressed badly, not sewn badly.
This one follows Mary from Joyful and Merry Quilting, who builds a nine patch and presses every seam a different way to see which lies flattest. Her answer involves a wool mat, a wooden pressing bar and a starch-filled marker pen. The rules underneath hold whichever direction you press.
Press means press. It does not mean iron.
Ironing is what you do to a shirt. The plate slides, the cloth travels under it, creases come out. Do that to a quilt seam and the cut edge stretches, because patchwork is full of bias and bias grows the moment heat and sideways pressure arrive together.
Pressing is lift, set down, hold, lift again. Ten seconds with the plate sitting still beats thirty seconds of scrubbing, and the row leaves the mat the same length it arrived.
Open or to the side?
Both are right, and quilters have argued about it for a century. To the side is the stronger seam, because the stitching never gets pushed apart from behind. It also leaves a ridge on one row and a groove on the next, and those opposing ridges are what let you nest seams at an intersection. Nesting is the easiest way to get points to match, and it only works if the two rows went in opposite directions. Press to the side and nesting is available. Press open and it is not. That is the trade.
Open lies flatter. No double thickness anywhere, so the surface stays even and the quilting needle never climbs a bump. If your piecing is dense, or you mean to quilt across the intersections rather than in the ditch, open is the better call. It is slower work, which is why Mary reaches for the marker and the bar. Whichever you choose, choose it per project and not per seam.
Press toward the darker fabric
Pressing to the side leaves one more decision. Send the allowance under the darker of the two squares. A dark allowance behind a pale square shows as a grey shadow once the quilt is washed, and nothing fixes it. Where both fabrics are the same value, press whichever way lets the next seam nest.
Dry iron, steam or starch
Steam is the fastest way to stretch a block. Water relaxes cotton, the plate bears down, and a square cut at three and a half inches leaves the mat bigger. Press dry and your units come out more consistent.
Starch does the opposite job. It stiffens the cloth so the seam stays where you put it. Spray your yardage before you cut the pieces and everything downstream behaves better. Mary skips the pre-spray so her test stays fair, then applies solution seam by seam with a refillable marker.
When a seam will not lie flat
Check the seam allowance first. If it came out wider than a scant quarter inch, there is more fabric folded behind the block than the block can absorb, and no amount of heat flattens it. Re-sew before you re-press.
A lump at an intersection usually means four layers of allowance stacked the same way. Open that seam, work the allowances apart with a wooden tool, and press it over a rounded bar so the bulk falls away from the seam line.
A block that rocks on the table has one allowance folded back on itself. Turn it over and look along the back. Fix it now, because once the block is sewn into a row that fold sits under a second seam.
Flat seams are what make everything after this possible. Trim with confidence when you square up the block, build a strip block like a log cabin without the centre going lumpy, keep the points on your half square triangles, and lay a quilt sandwich flat when you machine quilt it.
