It's not reverse applique---the technique in the block below for the star in the center and the holes in the leaves.
Block dated 1845
The flower and leaves are done in conventional applique. The oval holes in the leaves and the star in the center are done in reverse applique--- the calico is cut out to reveal the white background.
These are the more common mid-century techniques.
Sunburst quilt of Turkey reds on white, 1840-1870.
Collection of Laura Fisher
In conventional applique we apply the figures to the background---the visual background is the actual background. In this period style the visual background is the applique foreground. When you look closely at the red and white quilt above you can see that the sunburst is appliqued but it is not the spiky white points that are appliqued.
It's the red pie-shaped pieces that are appliqued atop the white.
The negative space in the design pops out.
Block dated 1848
These nine patch variations of a common block often called Bear's Paw were sometimes appliqued rather than pieced in the 1840s and '50s. In the example above, the quiltmaker began with white corner squares and appliqued 2 yellow triangles and one yellow square on top of the white.
Below is a deconstructed block I found. It's one of the appliqued corners. I hope you can see the tiny applique stitches.
To make this you'd need a white square for background and two brown triangles and a brown square to applique.
You'd make four such corners and then turn it into a nine patch.
Click here to see one in the collection of the International Quilt Study Center and Museum.
It's an album quilt dated 1847 from Byron and Sara Dillow's collection.
My guess on a pattern is:
For a 9" finished block
Cut 5 white squares 3 1/2" x 3 1/2"
Cut 4 dark squares 3 1/2" x 3 1/2"
For the corners cut
8 dark squares 1 3/4"
Cut 4 of these squares in half diagonally to make 8 triangles
Applique the dark pieces to the corners, turning under a small seam allowance.
Piece into a nine patch
It's the same principle in the Wreath of Hearts I appliqued several years ago.
The appliqued hearts disappear while the negative space, the background fabric, creates a sunburst.
Here's an unusual pattern that looks to be about 1850
It's a combination of negative and positive applique that was posted on an online auction recently..
The center floral shape is the white background showing through.
The applique there is the curved triangular pieces.
The four simple leaf shapes coming out of the corners are done in conventional applique.
You can see it's not reverse applique because those curved triangular shapes are laid down individually at least in the blue violet example above.
The pink block could be reverse applique, but I doubt it.
So if you are looking for an authentic Civil-War-era pattern think about an appliqued Bear's Paw Nine Patch.