This is just my never ending reminder about leaving some looseness in your sashiko thread on the back of your fabric.
I just put some new pre printed sashiko panels on the website and as always I worried about customers who may not know that they must leave some looseness in their threads on the back of the fabric as they stitch.
These panels worried me more than most because they have some quite dense areas of stitching, and will therefore be even more prone to puckering and bunching if your stitching is too tight.
And yes, too tight is what it is if when you pull your needle through you are pulling the thread out flat and smooth every time. It looks great at the beginning, but as your project goes on you may see some unhappy-making tightening in your earlier stitching!
Here is why. You are putting a lot of thick sashiko thread between the warp and weft threads of the fabric as you stitch. This is going to make the fabric bunch up as the stitching gets more dense. It has too, the width of that thread is forcing the threads in the fabric to push up against each other.
What to do about it: Leave some slack in your thread. In the photo below you can see I have left a loop of thread where I am turning a corner. Always do this! You can use the blunt end of your needle to pull these loops to the back every once in awhile.
In this photo you can see that I have left similar loops at every crossing. I'm leaving a lot of loops on this particular piece of fabric for two reasons. The stitching is very close together in places (very dense) and the fabric is quite tightly woven.
(Tip: for this particular panel, if you are ordering it from my website, I recommend choosing the Olympus 100 meter threads because they are thinner than the 20 meter threads, also the Tulip sashiko needles, either the short ones or the thin long polished ones)
As you continue to stitch these loops will most likely disappear by drawing themselves into the fabric. If they don't disappear, that is good too, they will act as insurance against the bit of shrink that happens in washing and drying over time. In fact I will leave an extra amount of slack (more than I am showing here) as I stitch this piece because I know I will wanted to wash it several times before making it into my final project, just to get that bit of wear and gentle pucker that makes hand stitched cloth so lovable :-D
Our sashiko fabrics and threads don't shrink noticeably, but even so, all fabric will tighten some, and the 100% cotton sashiko thread is intended to thicken and plump up with washings. If you have left enough slack in the stitching to allow the thread room to plump up without pulling the fabric your sashiko project will get much prettier with wear and washings.
Already found this out the hard way? Here is a fix of sorts. Cut through a stitch in the bunched area and work the stitching back through the fabric until the fabric is laying flat again, then re-stitch the area that is now empty of stitching. I weave my threads under a few stitches on the back to start and finish them when doing this. You may need to do this in several places if the bunching is bad.
Here is a basic sashiko tutorial showing more about this. It also includes a transfer method for putting designs on your own fabric, and a 'do and don't' basic sashiko stitching chart.
Apparently I have talked about this before in this blog also, which shows a sample of stitching a design from the back of the fabric