For the piano keys, cut:
10 strips (all from dark or med/dark fabrics) 1 1/2” x 16”
Stitch them together, side by side. Press all seam allowances in one direction.
Counter cut these units into 4 - 3 1/2” sections. These sections should measure 3 1/2” x 10 1/2”. Set these aside.
20 squares (all from dark or med/dark fabrics) 3 7/8”
Pair the 20 squares into 10 sets.
Draw a diagonal line on the wrong side of one of the squares in each set.
Stitch the two squares right sides together by stitching 1/4” on either side of the drawn line.
Chain stitch these to speed things up a bit.
Cut directly on the diagonal line.
Press the seam allowances towards the darker of the two triangles. This will result in 20 HSTs. At this point, they should measure 3 1/2”. You may need to square them up to that measurement.
Arrange 10 of the HSTs in one long strip. Stitch them together. Repeat with the other 10 HSTs.
On either end of the HST strips attach one of the piano key units that you made earlier. Repeat with the other two units.
Your completed border strip should measure 3 1/2” x 50 1/2”. Attach to the top and bottom of the quilt. Press the seam allowances toward the border.
There you have it! At this point, the quilt should measure 50 1/2" x 60 1/2"