The friend I was expecting today actually came yesterday (Saturday), so here I am on Sunday instead. That's kind of how life goes around here.
So, on to half-square triangles, or HSTs as they're commonly called nowadays. Simply, these are made by cutting two squares of fabrics A and B in half diagonally and then sewing the resulting triangles back together, pairing a fabric A with a fabric B. It's one of the simplest and most basic units of patchwork, but there are at least half a dozen ways to make them. I'm only going to cover a few of them here.
For this project, I started with 3-inch squares of light and dark fabrics. In the first method (top left in photo above), I folded the light square in half to make a creased line, placed the light square right sides together (RST) on the dark square, then sewed 1/4-inch from each side of the creased fold line. The squares are then cut on the creased fold line, creating two HSTs. This method is simple and low-tech, but requires good lighting and good eyesight. At my age, my near vision isn't as good as it use to be, and the lighting in my shed studio after dark is pretty minimal. I generally avoid this method now, but used it a lot years ago.
The second method (pictured top right) is very similar: the creased fold line is simply replaced by a pencil or pen line drawn with a ruler. This method is a bit more time-consuming, but the line is a lot easier to see! I used this method for years, starting with pencil lines at first, then later using fine-point, washable felt markers.
Lately, I've dispensed with the lines altogether and now use method 3 (pictured at bottom in photo above). I stack my light and dark squares right sides together, cut them diagonally, then sew the triangles together. As long as I'm careful to not stretch the bias cut of the triangles as I sew, this method is the speediest of the three. In my early days of patchwork, I produced a lot of wonky HSTs using this method so I switched to the first two methods. Experience, a better understanding of bias cuts, and the knowledge that
I'm not getting any younger, have made me brave enough use this method again.
Whatever the method, once the triangles are sewn together each HST unit must be pressed open. In most cases, place the dark fabric on top and then flip it over and press. This presses the seam toward the darker fabric and reduces the chances of it showing through. In some block patterns, the seams need to be pressed toward the light fabric in order to make all seams nest together later. In the "Sunrise, Sunset" block, all HST seams can be pressed toward the dark fabric.