If you love a quilt block that is easier to sew than it looks, the Mosaic Star is about to become a new favorite. This stunning 12″ traditional block achieves its striking effect using just three fundamental units (half square triangle, square in a square, and hourglass) making it perfect for quilters ready to level up without tackling advanced techniques.
Fabric Requirements for a 12″ Finished Mosaic Star Quilt Block:
- Light/White: 1 – 5.5″ square, and 2 – 5″ squares
- Medium/Aqua: 1 – 5.5″ square, and 1 – 4.5″ square
- Medium/Green: 2 – 5″ square
- Dark/Purple: 4 – 2.5″ squares
- Dark/Blue: 2 – 5.5″ squares
Sewing Directions:
Half Square Triangle Units:
Step 1:
Using a Light/White 5″ square and a Medium/Green 5″ square, make Half Square Triangle (HST) units as shown. Here are the steps corresponding to the images in the picture below going from left to right.
- Match up the squares right sides together. Mark a diagonal line from corner to corner on the back of the Fabric A square and sew 1/4″ (or a little less) on each side of the line.
- Cut along the diagonal line. You will have 2 half-square triangle patches.
Step 2:
- Open up the patch and press the seam allowance away from the Light/White fabric.
- Square up/trim the units to 4.5″ square.
- You can find my tutorial for making HST units at https://quiltembroiderypdf.com/how-to-sew-a-basic-half-square-triangle-block
Step 3:
Repeat Steps 1 and 2 for a total of Four HST units like the ones in the picture below.
Square in a Square Unit:
Step 4:
Using the Medium/Aqua 4.5″ square, and four Dark/Purple 2.5″ squares “snowball” the corners of the Medium/Aqua 4.5″ square. I like to work on two opposite corners at a time. Click Square in a Square for a detailed tutorial on making this unit. Here are the first steps:
- Mark a diagonal line from corner to corner on the back of the 2.5″ squares.
- Sew two Dark/Purple 2.5″ square to opposite corners of the Medium/Aqua 4.5″ square along the marked line. Note the orientation of the marked lines.
- Match the corners of the 2.5″ squares and press.
Step 5:
- Open up the 2.5″ squares and trim the seam allowances.
- Refold.
Step 6:
Repeat on the remaining two corners with two more Dark/Purple 2.5″ squares.
Hourglass Units:
Step 7:
- Using Steps 1 through 3 as a reference and using the two Dark/Blue 5.5″ squares, the Medium/Aqua 5.5″ square, and the Light/White 5.5″ square, sew together four Half Square Triangle units as shown in the picture below.
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Press the seam allowances toward the Dark/Blue fabric. No need to trim/square up these units at this time as we will trim in a later step.
Step 8:
Using two of the Step 7 half-square triangle units (one of each coloring) make two three-color Hourglass units as shown below.
- Match the two half-square triangle patches, right sides together, and rotate one of the patches 180 degrees so the Dark/Blue sides are opposing each other and the seam allowances nest together nicely.
- Mark a diagonal line on back of the patches perpendicular to the seam line. This is more accurate than drawing a line from corner to corner.
- Sew ¼” (or a little less) on both sides of the diagonal line.
- Cut on the diagonal line.
Step 9:
- Open up the units and press seam allowance toward the Medium/Aqua & Dark/Blue side. At first I pressed using the tweak/twirl/furl method but that didn’t work for later on in the piecing.
- Trim/square up the units to 4.5″ square.
- You can find a detailed tutorial for making the three-color Hourglass block at https://quiltembroiderypdf.com/how-to-sew-a-basic-hourglass-or-quarter-square-triangle-block
Step 10:
Repeat Steps 7 through 9 for a total of four Hourglass units like the ones shown in the picture below.
Putting It All Together:
Step 11:
Lay out the Step 3 Half Square Triangle units, the Step 6 Square in a Square unit, and the Step 10 Hourglass units as shown in the picture below. From here the block goes together like a typical Nine Patch block.
Step 12:
Sew the units into three rows.
Step 13:
Press the seam allowances away from the Hourglass units as shown in the picture below.
Step 14:
Sew the three rows together and…
Step 15:
Press the seam allowances toward the center of the block.
Layout Ideas:
Here is the basic 4 x 4 layout using colors similar to the tutorial.
And this is the same layout as above but with narrow (1″) sashing and cornerstones added.
This is an example of an alternating layout where every other block is a Snowball block. Traditionally, the Mosaic Star was done in only a light and a dark fabric – as shown here.
Another alternating design using a simple chain block for the alternate block.
This is an on-point layout with coordinating narrow sashing and cornerstones. The light fabric is used for the setting triangles.
Here’s another on-point design with a chain block being used as an alternating block that also extends into the setting triangles.
