block stability
 

I have been given some old blocks to make into a quilt. Some of them are rather thin. Should I put some interfacing or muslin on the backs to make them more stable? None of the blocks have holes or tears but just rather thin. Thanks.

I bought some old blocks at a quilt show and put a light weight fusible on mine. also you might starch them to give them more stability when sewing them.

I am not a big fan of fusible interfacing, but it is easy to use. If you really feel they need some extra "support", I would buy some thin muslin (PREWASH IT BEFORE USING as it can shrink a lot), cut it into squares the same size and stitch them to the outer edges of the blocks. But this will add weight to the finished quilt, which may or not be a concern for you.
Keep in mind that the stitching of the quilting will add a lot of stability to those blocks, and of course the heavier the quilting design the more support the blocks will have.
I guess one last thought, is your concern about the thinness of the fabric quality, or the potential for the seams to come undone as the quilt is used? Fusible interfacing may be of more help it the fabric itself is thin, but adding muslin and more dense quilting may be more helpful if it is the long-term fastness of the piecing that you are worried about.

Either interfacing or muslin would work in the short-term and mid-term. Because the blocks are vintage, I would probably opt for a thin, pre-washed muslin because it will support the blocks long-term. Fusible interfacing has more unknowns associated with it. Some might be fine, but others may eventually shred inside the sandwich and stop providing support.

Are these blocks to be made into a quilt for yourself, or for someone else?

I wouldn't use Pellon for that reason. There are some nice fusibles made to use with silks that are very thin and non-Pellon products. I'd use one of those.

Good ideas, but if the fabric wasn’t shrunk, the starch will cause shrinkage, so you might want to test one to check for shrinkage. I tried starch on precuts...it so, so, so didn’t work due to shrinkage.