Diffraction Block Tutorial

Note: This tutorial was originally written in partnership with OLFA and published on the OLFA craft blog, which no longer exists.

I love all the angles included on the OLFA 6″ x 24″ Frosted Acrylic Ruler, and they inspired me to create the dramatic Diffraction Quilt Block. The Diffraction Quilt Block is created using a repeated slice and insert progression. Careful trimming after each sewn seam is the key to accurately piecing the block. The block is also perfect for learning to fine tune sewing a consistent ¼” seam allowance.

I have also successfully made this block using the 6½” x 24″ Omnigrid acrylic ruler. Note that the Omnigrid ruler does not contain a 15 degree line, so not all of the directions here will translate exactly, but keep turning the ruler, it is possible to make all the cuts!

Suggested Supplies

• Sewing Machine
• Thread
• Fabric Safe Removable Marker
• Iron
• OLFA Rotary Cutter
• OLFA 18″ x 24″ Rotary Cutting Mat (or larger)
• OLFA 6″ x 24″ Frosted Acrylic Ruler
• OLFA 12½” Square Frosted Acrylic Ruler

General Tips

• Skill level: Intermediate
• Sew all seams with a scant ¼” seam allowance
• Press all seams toward the Ray Fabric (white)
• Read through the entire project instructions prior to beginning
• WOF = Width of Fabric
• RST = Right Sides Together

Fabric Required for (1) Diffraction Quilt Block

• Background Fabric (Kona Cotton Nightfall)
  • (1) 12″ square
• Ray Fabric (Kona Cotton White)
  • (1) 1″ x 17½” rectangle
  • (2) 1″ x 14″ rectangles
  • (2) 1″ x 12½” rectangles

Ray 1

With the 6″ x 24″ ruler, align the 45° line along one side of the Background 12″ square.

Make sure that the corner of the 12″ square aligns with the edge of the 6″ x 24″ ruler and 45° line. The 6″ x 24″ ruler should pass through opposing corners of the 12″ square.

Using a rotary cutter, cut along the 6″ x 24″ ruler to cut the 12″ square in half on the diagonal, making 2 triangles.

Right sides together (RST), align one edge of the Ray Fabric 1″ x 17½” rectangle with one background triangle (along the edge that was just cut). Sew together with a scant ¼” seam allowance and press the seam toward the Ray Fabric.

Note that the edges of the cut background fabric are bias cuts, so care should be taken not to stretch or distort the block as it is sewn. The length of the 1″ x 17½” rectangle is generous, so aim to have an even amount of fabric overhanging each edge when positioning prior to sewing.

Using the 12½” Square Frosted Acrylic Ruler, align the top with the edge of the ruler and left-hand side of the pieced unit with the 12″ line. Use your OLFA Rotary Cutter to trim the Ray Fabric on the right and top.

Rotate the pieced unit and align the right-hand side with the edge of the ruler and the bottom with the ruler’s 12″ line. Trim the Ray Fabric on the right and top.

Align the edge of the second Background Fabric triangle RST with the Ray Fabric rectangle such that the second background triangle is centered on the ray fabric triangle. Sew together with a scant ¼” seam allowance and press the seam toward the Ray Fabric.

After pressing the seam open, verify that the sewn Ray Fabric strip is ½” wide.

Using the 6″ x 24″ ruler, align the ¼” marks with one edge of the Ray Fabric strip and using a fabric safe marker, mark the center of the Ray Fabric. Note I like to use a Hera Marker to mark this line, but for the purposes of this tutorial, I used a pencil so the mark would be visible through the rest of the tutorial.

Carefully align the 45° line on the 12½” square ruler with the halfway mark on the Ray Fabric, and square the pieced block to 11¾”. Make sure that the 11¾” marks on the ruler go beyond the bottom and left-hand edges prior to making the first two cuts so that the block can be rotated and trimmed on all 4 sides. Trim the block on the right and top.

Rotate the block and align the bottom and left-hand edges with the 11¾” lines. Trim the block on the right and top.

Ray 2

Align the 60° line on the 6″ x 24″ ruler with the left-hand edge of the block.

Make sure the edge of the ruler and 60° line intersect at the corner with the Ray Fabric.

Using a rotary cutter, cut along the 6″ x 24″ ruler to cut the square into two units.

Tip: To reduce seam bulk, gently seam rip and remove the ray fabric from the tip of the smaller, lower unit.

Align one edge of a Ray Fabric 1″ x 14″ rectangle RST with the larger of the two units that were just cut. Sew together with a scant ¼” seam allowance and press the seam toward the Ray Fabric.

Note that the length of the 1″ x 14″ rectangle is generous, so aim to have an even amount of fabric overhanging each edge when positioning prior to sewing.

Aligning the top with the edge of the ruler and the left-hand edge with the 11¾” line on the 12½” ruler, trim the right-hand side of the block.

Align the edge of the second unit RST with the Ray Fabric rectangle.

Align the top triangle such that the “V” formed by the overlap is ¼” away from the edge, that way your needle will intersect with the point of the “V” when you stitch the seam. Sew together with a scant ¼” seam allowance and press the seam toward the Ray Fabric.

Carefully align the 45° line on the 12½” square ruler with the halfway mark on the Ray Fabric, and square the pieced block to 11½”. Make sure that the 11½” marks on the ruler go beyond the bottom and left-hand edges prior to making the first two cuts so that the block can be rotated and trimmed on all 4 sides, but the goal should be to trim as little from the bottom and left-hand edges of the block as possible. Trim the block on the right and top.

Rotate the block and align the bottom and left-hand edges with the 11½” lines. Trim the block on the right and top.

Ray 3

Align the 15° line on the 6″ x 24″ ruler with the bottom edge of the block.

Make sure that the center of the ruler and 15° line intersect at the corner with the Ray Fabric.

Using a rotary cutter, cut along the 6″ x 24″ ruler to cut the square into two units.

Tip: To reduce seam bulk, gently seam rip and remove the ray fabric from the tip of the smaller, lower unit.

Align one edge of a Ray Fabric 1″ x 12½” rectangle RST with the larger of the two units that were just cut. Sew together with a scant ¼” seam allowance and press the seam toward the Ray Fabric.

Note that the length of the 1″ x 12½” rectangle is generous, so aim to have an even amount of fabric overhanging each edge when positioning prior to sewing.

Aligning the top with the edge of the ruler and the left-hand edge with the 11½” line on the 12½” ruler, trim the right-hand side of the block.

Align the edge of the second unit RST with the Ray Fabric rectangle.

Align the top triangle such that the “V” formed by the overlap is ¼” away from the edge, that way your needle will intersect with the point of the “V” when you stitch the seam. Sew together with a scant ¼” seam allowance and press the seam toward the Ray Fabric.

Carefully align the 45° line on the 12½” square ruler with the halfway mark on the Ray Fabric, and square the pieced block to 11¼”. Make sure that the 11¼” marks on the ruler go beyond the bottom and left-hand edges prior to making the first two cuts so that the block can be rotated and trimmed on all 4 sides, but the goal should be to trim as little from the bottom and left-hand edges of the block as possible. Trim the block on the right and top.

Rotate the block and align the bottom and left-hand edges with the 11¼” lines. Trim the block on the right and top.

Ray 4

Align the 30° line on the 6″ x 24″ ruler with the left-hand edge of the block.

Make sure the edge of the ruler and 30° line intersect at the corner with the Ray Fabric.

Using a rotary cutter, cut along the 6″ x 24″ ruler to cut the square into two units.

Tip: To reduce seam bulk, gently seam rip and remove the ray fabric from the tip of the smaller, upper unit.

Align one edge of a Ray Fabric 1″ x 14″ rectangle RST with the larger of the two units that were just cut. Sew together with a scant ¼” seam allowance and press the seam toward the Ray Fabric.

Note that the length of the 1″ x 14″ rectangle is generous, so aim to have an even amount of fabric overhanging each edge when positioning prior to sewing.

Aligning the top and right-hand edge with the sides of the ruler and the bottom edge with the 11¼” line on the 12½” ruler, trim the top of the block.

Align the edge of the second unit RST with the Ray Fabric rectangle.

Align the top triangle such that the “V” formed by the overlap is ¼” away from the edge, that way your needle will intersect with the point of the “V” when you stitch the seam. Sew together with a scant ¼” seam allowance and press the seam toward the Ray Fabric.

Carefully align the 45° line on the 12½” square ruler with the halfway mark on the Ray Fabric, and square the pieced block to 11″. Make sure that the 11″ marks on the ruler go beyond the bottom and left-hand edges prior to making the first two cuts so that the block can be rotated and trimmed on all 4 sides, but the goal should be to trim as little from the bottom and left-hand edges of the block as possible. Trim the block on the right and top.

Rotate the block and align the bottom and left-hand edges with the 11″ lines. Trim the block on the right and top.

Note that in addition to aligning the 45° line on the 12½” square ruler with the halfway mark on the Ray Fabric, the 45° line should now also pass into the seam line point of the first pieced Ray Fabric, as shown above.

Ray 5

Align the 15° line on the 6″ x 24″ ruler with the left-hand edge of the block (rotated to appear as the bottom edge of the block as shown above). Make sure that the center of the ruler and 15° line intersect at the corner with the Ray Fabric.

Using a rotary cutter, cut along the 6″ x 24″ ruler to cut the square into two units.

Tip: To reduce seam bulk, gently seam rip and remove the ray fabric from the tip of the smaller, lower unit.

Align one edge of a Ray Fabric 1″ x 12½” rectangle RST with the larger of the two units that were just cut. Sew together with a scant ¼” seam allowance and press the seam toward the Ray Fabric.

Note that the length of the 1″ x 12½” rectangle is generous, so aim to have an even amount of fabric overhanging each edge when positioning prior to sewing.

Aligning the top and right-hand edge with edge of the ruler and the bottom edge with the 11″ line on the 12½” ruler, trim the top of the block.

Align the edge of the second unit RST with the Ray Fabric rectangle.

Align the top triangle such that the “V” formed by the overlap is ¼” away from the edge, that way your needle will intersect with the point of the “V” when you stitch the seam. Sew together with a scant ¼” seam allowance and press the seam toward the Ray Fabric.

Final trim the block to 10½” square, starting with the corner where all the Ray Fabrics intersect.

Align the 12½” square ruler 45° line with the marked line on the Ray Fabric and adjust the ruler until the transition from the Ray Fabric and Background Fabric falls at 1½” on both the top and right-hand side of the ruler.

Make sure that the 10½” marks on the ruler go beyond the bottom and left-hand edges for the first two cuts so that the block can be rotated and trimmed on all 4 sides. Trim the block on the right and top.

Rotate the block and align the bottom and left-hand edges with the 10½” lines. Trim the block on the right and top.

View of the back of a Diffraction Quilt Block.

There are many fun ways to combine and use a Diffraction block, and I look forward to seeing how it sparks your creativity! Below I am linking to other projects that have incorporated the Diffraction Block.

• Pansy Challenge (Mini Quilt)
• Cindy from Hyacinth Quilt Designs Created a fun, offset mini using the Diffraction Block
• Memorium: Speech Acts for a Dying World by Elisabeth from Occasional Piece Quilt