I want dark green thread on the top of my quilt, and white on the back. Why can’t you do this?
Actually, while this can be done, I usually advise against using two different thread colors for longarm quilting as you might not be very happy with the outcome. With a longarm quilting machine, we are moving the machine around in all directions over the quilt sandwich at a high rate of speed. As we change direction, the thread tension often changes slightly as well. Ideally, the portion of a stitch where the top and bobbin thread meet will lock exactly in the center layer of the batting, but this is not always the case. Then you end up with what we longarmers call ‘pokies’ – little dots of the top thread showing on the backing, or bobbin thread showing on the top of the quilt sandwich. When you use two thread colors that differ widely, these ‘pokies’ are very pronounced.
Here is a design stitched with green thread on white fabric – pretty, isn’t it? (Panto is Holly & Bows Pantograph 3 by Donna Kleinke of One Song Needle Arts.)
What happens when we use a contrasting thread in the bobbin? Now the back of the quilt is not very attractive, right?
(Sometimes we can minimize the effect by using a thinner thread, or a high loft batting. So if you have your heart set on contrasting thread colors, choose a loftier batting.)
Normally when I explain this to a client, and show them a sample of what can happen, they agree with me to use the same color thread on top and in the bobbin. After all, if you were hand quilting your quilt, and using white thread on top, what color would you use on the back???????