Two ten inch squares go under the needle on the diagonal, come out as one large half square triangle, and get pressed. What happens in the next two minutes decides whether the rest of the block behaves itself. The temptation at that point is to reach straight for the crosscuts, because the unit looks finished and the cutting instructions are sitting right there. The unit is not finished. It is roughly nine and a quarter inches of fabric with edges wherever the seam and the iron happened to leave them, and it is about to be measured from.
Square it to nine inches first, before any other cut is made. Lay the forty five degree line of the ruler along the diagonal seam rather than lining the block up by its outer edges alone, because that is what sets the seam at a true forty five degrees to the sides rather than merely making the outside measure nine by nine. A unit can be exactly nine inches square and still have its diagonal running off at a slight angle, and that angle is the thing that will refuse to match when the pieces are turned and rejoined.
Only then do the rest of the cuts happen, and they happen in a fixed order. Four and a half inches in the vertical direction, four and a half in the horizontal, and then two and a quarter inches in from two of the sides. Every one of those measurements is taken from a square you have already made reliable, which is the whole point of the sequence. Cut first and square later and each of the nine pieces carries a share of whatever the original edge was doing, and there is no way to correct it afterwards, because the pieces have been rearranged and the reference edge no longer exists.
The arithmetic at the end is what tells you the order worked. Rejoining the pieces costs half an inch in each direction, two seams at a quarter inch each, so nine inches becomes eight inches unfinished and seven and a half finished. Those numbers only arrive if the quarter inch allowance was genuinely there at every seam, and it is only there if the pieces were the right size when they were cut. That is why a block trimmed in this order comes out predictable, while the same block cut in a hurry comes out somewhere between seven and a quarter and seven and three quarters and nobody can say quite where the difference went.
Blocks in this family have a reputation for producing a great deal of bias, and it is deserved in most cases, because the usual method recuts a pieced unit along its diagonal and leaves you holding edges that stretch under their own weight. This one avoids nearly all of that. Every cut after the squaring runs parallel to the sides of a block that is already true, so each new edge lands on the straight of grain. The only bias in the whole block is inside that first diagonal seam, and by the time the crosscuts begin, that seam has been sewn, pressed and enclosed. It is a great deal of stability for a block that looks as though it should be fighting you.
Pressing follows one rule with one exception. The first diagonal seam goes towards the darker fabric, which keeps it from shadowing through the lighter side. Every seam after that is pressed open. The pieces come back together in a nine section arrangement where several seams converge, and open seams are what stop those junctions from turning into a hard ridge that the ruler then rides over the next time you measure.
Here is the sequence to keep at the cutting mat:
- Square the half square triangle to nine inches before any other cut. Nothing else in the block is measured from the original ten inch squares. Everything is measured from this one trimmed unit, so it is the only piece in the whole process that has to be right on its own terms.
- Set the forty five degree line on the seam, not just the edges on the numbers. The ruler line goes along the diagonal, and the nine inch marks fall where they fall. If the two do not agree, the seam wins and the outside edges get trimmed to suit it.
- Cut four and a half inches in both directions next. Vertical and horizontal, from the squared edges, before anything narrower is attempted. These are the cuts that establish the middle of the block, and they are the ones most exposed if the edge underneath them was not true.
- Then take two and a quarter inches in from two of the sides. Two sides only, and from the same reference edges you have been working from throughout. Changing which edge you measure from partway through is the quiet way this block goes wrong.
- Press the diagonal to the dark and open everything after it. One seam towards the darker fabric, every subsequent seam open, so the convergence at the centre lies flat and the block measures what it actually is rather than what the ridges make it.
- Check at eight inches before the block meets its neighbours. Eight unfinished, seven and a half finished. A block that arrives at eight has kept its quarter inch allowance at every seam, and a block that does not has told you something useful while there is still time to look at the seam allowance rather than the block.
Seeing the cuts made in order, with the ruler placed and the pieces turned before they are rejoined, makes the logic of the sequence clearer than the measurements on their own:
What makes a block predictable is almost never the sewing. It is the order in which the decisions were taken, and whether each one was made from something already known to be true. Square first, measure from the square, and the quarter inch you promised at the start is still there at the end. Nothing about that is dramatic, and it is the difference between a pile of blocks that go together without argument and a pile that has to be negotiated with one seam at a time.
The block begins with two ten inch squares, which is exactly what a layer cake gives you, and the pairing is part of why it works so well: two prints, one diagonal seam, and a finished block on the other side of it. Our layer cakes come precut at that size, so a pack lets you sew a whole quilt's worth of these without cutting a single starting square. Do give them a measure before you begin, as we would say of any precut, because squaring to nine inches has a little room in it and it is worth knowing how much of that room you actually have.
