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Mosaic 3 Quilt Block

From our Free Quilt Block Patterns Library

Mosaic #3 Quilt Block tutorial

Skill Level: Confident Beginner
Grid: 4x4

The Mosaic 3 quilt block is from a family of blocks where all the patches are on point.

Because of this, the measurements are typically unfriendly for rotary cutting. Lots of fudging and guesstimating going on.

To make this block we offer two alternatives. Low cost—using templates printed directly from this page—and some cost—using a specialty ruler that makes cutting the on-point, weird-math patches easy as pie!

Let's get started!





Special Note

If you've come to this page from our Deconstructing Antique Quilt Designs series, note that the background and dark fabrics in the cutting charts are reversed for our antique quilt design.

Click here to read my confession about the making of the sample block.


Construction Instructions

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While it's not often that I write instructions that recommend a specialty ruler, the On Point (by Donna Lynn Thomas) makes creating this block really easy—especially if you're making a lot of them.

Templates are also included if you don't want to add to your collection of quilting rulers. (The links to print them from are in the cutting instructions below.)

Because of the many bias edges in this block, I highly recommend starching your quilt fabric. Starch helps tame the bias and minimize the stretching out of shape as you stitch.

All the seams run diagonally through this block so an exact quarter inch seam is a must. A quick sewing test before you start will help you check the accuracy of your seams before you begin.

All seam allowances (SA) are a 1/4".


Step 1: Cutting Instructions

Choose the cutting option that best suits your situation.

Option 1: Using a template

Choose your block size and then print the corresponding template page from the table below. 

Mosaic #3 quilt block designMosaic 3 Quilt Block

If you've never downloaded and printed patterns from this website, click here for instructions so that each template is printed at the correct size.

Check that the 1" box on the template page is exactly one inch.

Then cut out #1, #2, #3 and #4. There's no need to cut exactly on the line—we'll clean things up when we use our rotary cutter.

#3 and #4 are exactly the same shape and size. You will use them for two different fabrics.

The arrows indicate the fabric grainline and should be placed on your fabric so that they are parallel to the selvedge edge. This makes the blocks more stable. At an absolute minimum, the #1 and #2 triangle patches should be 'on-grain' to make the block's outside edges stable.

For your Mosaic quilt block you'll need the following quantities:

  • Four background #1's - half square triangles
  • Four background #2's - quarter square triangles
  • Four Dark #3's - squares
  • One background #4 - square

Remember that dark is a relative term—you need even contrast between the #3's and the rest of the patches for your piecing to show—otherwise why bother to piece the block?

On your cutting mat, lay the template printed side up on your fabric. The paper can be a bit slippery, so I use Scotch® Brand Magic™ Tape (it doesn't leave behind a residue) to tape the templates to the top layer of fabric.

You need a 1/4" seam allowance past the solid outline of the template. Though there is a dashed line to indicate where to cut, I find it SO MUCH EASIER and FASTER to place the 1/4" mark on ruler directly on top of the solid line on one side of the template (red arrow below).

Trying to match the edge of a ruler with that dashed line is just a pain in the you-know-where!


Align the 1/4You can just make out the tape I used to hold the template in place.

Cut. Repeat for the remaining three sides of this #3 template.

To save time, I use a rotating rotary mat and turn it instead of the fabric. Between this and the tape, there's almost no time spent re-positioning templates.


Cut another side of the patchThere's another piece of Magic™ Tape.

Once your patches are cut, click here to skip to Step 2.


Option 2: Using an On-Point plus a standard ruler

The Mosaic #3 quilt block designMosaic #3

Choose your block size from the table below and cut the patches indicated.  You'll need your regular ruler for #1 and #2.

#3 and #4 are cut with the On Point Ruler.

If you do not have one, print appropriate templates for Option #1.

The numbers in the chart represent squares, i.e. 1-7/8" means to cut a 1-7/8"x1-7/8" square.

Don't forget to subcut your #3 and #4 patches.

CUTTING CHART for a
Mosaic #3 Quilt Block
Finished Block Size
Patch
#
Fabric Qty 4" 6" 8" Sub
Cut
1 Background 2 1-7/8” 2-3/8” 2-7/8” Symbol for a half square triangle
2 Background 1 3-1/4” 4-1/4” 5-1/4” Symbol for a quarter square triangle
3** Dark 4 2” 3” 4” na
4** Background 1 2” 3” 4” na
Unfinished Block Size 4 1/2" 6 1/2" 8 1/2" ---
Grid Size 1" 1 1/2" 2" ---
**MUST CUT with the On Point Ruler

Step 2: Assemble the rows of the Mosaic 3 quilt block

Arrange the patches as shown below.

Take care that the #2 quarter square triangles (QST) are on the sides and the #1 half square triangles (HST) are in the corners. This insures that the outside edges of the blocks are on straight of grain. They'll be less likely to stretch out of shape.


The patches laid out in the design of the block


Starting with the upper left #3 square, pin a #2 QST to one side so that the straight edges will feed into your sewing machine first (red arrow).


Pin #2 to #3 matching the straight edges.Stitch starting at the red arrow.

Stitch. From the #3 side you can see that the 1/4" seamline is slightly to the left of the valley created by the two patches. This is correct.


The seam line is a bit to the outside of the valley created between the two patches


Stitch and press with the SA towards #2 QST.

Add a #2 QST to the opposite side of this orange #3 in the same manner. Again, you can see that the QST extends just a wee bit beyond the bottom of the #3 patch. This is correct.

A #3 squares with a #2 QST sewn to each side


To find the center of the #3 and a #1 patch, fold them in half and fingerpress a crease into the fold.

With RST, match center (fold) of the #1 HST to the center (fold) of the #3 unit. Pin.


Fingerpress a crease to mark the centersFingerpress a crease into the center of the edges of the #1 and #3

With RST match the fingerpressed fold of the #3 to a #1. Stitch. This time your 1/4" seam should fall exactly at the bottom of the valley created by the patches (red arrows).



Press towards the #1 HST (red arrow).

The outside edges of the #1 and #2 triangles should create a straight line. If they don't, it's a sign that your seam allowance is off somewhere. Adjust it as necessary.


Just need to trim away the dog ears.

For the center diagonal row, with RST stitch a #3 dark square to opposite sides of the #4 background square, pressing the SA toward the #3s.

Find the center of the end of each #3 and fingerpress a crease to mark it as we did before. Do the same for the two remaining #1 HST.

With RST, match a creased #1 to a #3. Stitch. Repeat for the other #3. Stitch. Press the SA towards the #3s.


The patches stitched into diagonal rowsDogs ears are trimmed off either now or after the rows are joined.

Pin the rows together. The seams will nest making matching easy.

Stitch.


Stitch the rows togetherIf your seam allowances are accurate, your quarter inch seam will start exactly in the valley created by these two rows (red arrow).

The SA can be pressed in either direction.

Give your Mosaic #3 quilt block a final press using my favorite technique for pressing quilt blocks and you are finished!



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