Riley Blake Chain Reaction - Downloadable PDF

Chain Reaction Quilt Pattern by Sandy Gervais – Riley Blake Designs

Chain Reaction is a downloadable PDF quilt pattern designed by Sandy Gervais and published by Riley Blake Designs. This free pattern is rated as intermediate in difficulty and is built around a single, versatile block that can be arranged in a remarkable variety of layouts. Whether you are drawn to a structured, graphic look or a more relaxed scrappy aesthetic, Chain Reaction delivers impressive visual results from one foundational block construction.

What Is Being Made

The finished project is a patchwork quilt constructed from repeating Chain Blocks. These individual blocks are then grouped into larger Cross Blocks using sashing strips and a center square. The Cross Blocks are sewn together into rows, separated by additional sashing rows and connector squares, and finished with a simple border. The pattern provides two distinct quilt layouts as starting points, though Sandy Gervais notes that these are just a couple of the many possible arrangements that can be achieved with this one block.

• Quilt Layout 1 – A more structured design that groups four Chain Blocks of the same color together to create a bold, repeating pattern across the quilt top.
• Quilt Layout 2 – A scrappier arrangement that mixes colors more freely, resulting in a livelier, less uniform appearance.

The pattern also hints at further design possibilities by noting that removing one Corner square from the standard block opens up even more layout options, giving quilters creative flexibility well beyond the two featured layouts.

Block Construction and Techniques

The Chain Block is the heart of this pattern. Each block is composed of just two types of pieces: one Base Square and two Corner Squares. Despite its simplicity, the block produces a dynamic chain-like visual effect when blocks are combined across the quilt surface.

Half-Square Triangle Technique – Stitch and Flip

The primary piecing technique used to construct the Chain Block is the classic stitch-and-flip method, also known as the snowball corner technique. A diagonal line is drawn on the wrong side of each Corner Square before sewing, allowing the quilter to stitch precisely along the marked line and then fold back the corner to create an angled seam without cutting away fabric until trimming. This is a beginner-friendly technique within an intermediate-level pattern, making the block itself approachable while the overall layout planning adds the design challenge.

Sashing and Cross Block Assembly

Once individual Chain Blocks are pieced, they are grouped into sets of four and joined with background sashing strips and a center square to form larger Cross Blocks. The pattern suggests a finished sashing strip width of 2 inches (cut at 2½ inches to include seam allowance), though quilters can adjust this proportion to suit their preferred block size. Sashing rows are constructed separately by sewing sashing strips and connector squares together, then these rows are inserted between the block rows to create an even, lattice-like grid across the quilt top.

Scalable Block Sizing

One of the practical strengths of this pattern is its scalable block system. The cutting table provides formulas using a variable x to represent the desired finished block size, so quilters can adapt the pattern to work with pre-cut fabric stackers or their own preferred dimensions. Two specific finished block sizes are listed as examples:

• 4½-inch finished block – Base Square cut at 5 inches; Corner Squares cut at 2¾ inches.
• 9½-inch finished block – Base Square cut at 10 inches; Corner Squares cut at 5¼ inches.

The general formula is: Base Square cut at x + ½ inch, and Corner Squares cut at (x ÷ 2) + ½ inch, making it straightforward to calculate cuts for any desired finished size.

Stitches and Quilting Techniques

• Straight stitch – Used throughout all piecing, including the stitch-and-flip corner construction and all sashing assembly.
• ¼-inch seam allowance – All measurements in the pattern include a standard quilting ¼-inch seam allowance, which is