If you’re just beginning a medallion, you may already have a center block in mind. Perhaps there is an old traditional block you’ve always wanted to try, like a feathered star. Or maybe a modern log cabin setting has you excited. Did you receive a beautiful block in a swap but not figured out how to use it? If you’d like some other ideas, see my post A Center Block for a Medallion Quilt.
Here are a few considerations as you begin. First, the center is the focal point of the quilt. It does not need to be spectacular to serve that purpose, but it does need to be eye-catching. Many of my centers are fairly ordinary blocks such as variable stars, Ohio stars, or churndash variations. Bold is more important than fancy.
Second, the block should be sized appropriately for your goal. In general, you may want the center to be a quarter to half the width of the finished quilt. If it isn’t, there are ways to enlarge it while retaining the flavor of the block. I discussed size in Lessons: Starting a Medallion Quilt and in Proportion, Part 1.
Third, it’s very helpful if the block has good variations in color and/or value. I once made a block that had three main colors, teal, salmon, and red. All three had small prints with colors that were hard to pick out. All three were similar value. It was very difficult to find ways to expand the range and make it interesting.

Oh my! All the same value, and hard to pick out more colors…
As you look at the block above, you might note a fourth factor: shape. All the discernible shapes are squares, though in truth the red patches are non-square rectangles. Even the shapes aren’t interesting here. The diagonal lines created by the salmon squares is the only thing that saves this from being completely weird/ugly/disastrous. Well, it is those, but I rescued it…

Sparkle. 48″ square. Finished January 2014.
The shapes are important not just for how interesting the center is. The shapes also play into the fifth factor. Is the center block enclosed or expansive? Lines that direct the eye outward tend to make the block expansive. Diagonal lines tend to do this but aren’t the only way. Triangles and star shapes often create natural movement outward. In the block above, other than the salmon squares, there is no line that directs the eye beyond the block itself, and they don’t do a very good job of it. I would call that block enclosed.
Here are a couple more examples.

I Found the Housework Fairy But She’s Not Coming Back. 35″ square. June 2015. Photo by Jim Ruebush.

The Big Block Quilt. 84″ square. February 2016. Photo by Jim Ruebush.
In the Fairy, the center block is enclosed. Though we can imagine the scene extends beyond the frame, we really are called to look inward to the fairy herself, not outward. In the Big Block Quilt, the center is expansive. The outward-pointing flying geese, set in slightly paler gold for emphasis, literally radiate from the center.
Neither one is better ultimately. It is just a design aspect to understand for how it fits into your whole quilt. If your center is expansive, at some point you may need to contain it, as the first broad strip border does for the Big Block. If your center is enclosed, you might want to find a way to direct attention outward and provide some sense of movement. In Sparkle, above, the borders including the large red triangles serve that purpose.
Blocks set on point are expansive naturally, because of the long diagonal lines created. Look at the difference between this

and this.

The top one is more neutral than either expansive or enclosed. Though the brown triangles of this churndash block provide some visual movement, it is largely stopped by the blue and gold print at the center edges. Once it is turned on point, the strong blue diagonal lines push the eye to the outer edges of the block, where the brown unpieced border stops it again. This example has fancy corners added, but there’s no need to do extra piecing in the setting corners. See my post on when to set your block on point.
Finally, the examples here all show square centers. While they are easier, perhaps, there is no reason not to use a non-square rectangle. Some of my favorite quilts have non-square centers.
All of this makes it sound like choosing a center block is very complex. In fact it’s not. How should you choose a center block? Just pick something fun, or beautiful, or the right colors, or sentimental. As you saw with my weird/ugly/disastrous block above, there is no wrong block. They all can work.
Next comes borders. They all support the center and each other, but first borders have a little different role than last borders. And look for more Medallion Lessons here.