Find out fiber composition in thread?
 

Some years ago, my MIL gave me several old bobbins of thread, I guess they came from the inventory of FIL's shoemaker's workshop.
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(Apart from those on the picture, there are several more with white thread, and one brown.)

If I could be sure this would be 100 % coton thread, I would like to use it for handpiecing, but there isn't any information about the composition on the bobbins. It only tells me most are made in Belgium by the 'Filature & filteries réunies', and there are 500 yards on a bobbin (strange, that it gives the length in yards - and only on some bobbins in meters), and a number that seems to indicate the thicknes of the tread (going from 10 for the rather coarse beige thread on the largest spool, to 30 on the white and green thread, and 36 and even on different hues of brown (but two different hues have both 36, and I have a spool of the same shade of brown - but slightly different thickness - with 36 and 40)

But for the composition...
I seem to remember that there is a way to find out if a fiber contains coton, wool or polyester, by burning a piece of thread... By the smell and by the look of the ashes you could then determine which fiber you have. Anyone who knows more about this?

If the yarn is 100% coton, I'd like to use it for handpiecing, but if it contains polyester, I'd rather not use them...

I just found out something that might give me a clue (apart from burning the thread):
The spool on the right, with the dark green thread, is from another company, 'Wallaert Frères' in Lille, France. And I found on Etsy a cardboard box, used for the packaging of this 'Cable Louis d'or 6 fils' that is on the spool, and it says it is cotton!

http://www.etsy.com/listing/16223581...t-freres-lille

if you burn the end of polyester it will 'melt' become a hard ball of melted plastic. cotton and other natural fibers simply burn, turn to ash, fall away. I do not understand why you would not use polyester thread- since it's pretty commonly used in quilting- but what ever- your choice. personally I would do a strength test & if the thread is strong I would use it- although I doubt that I would use it for piecing since it is such a heavy thread. (most of us use somewhere between 40wt and 60wt thread for piecing) threads that heavy I would use for big stitch quilting, decorative stitching or for other applications (like sewing on buttons- toy construction, pillows-- sewing outside of quilting)

Thanks for your help! The thread seems to be cotton.

Why I don't use mixed fiber or polyester?
Most polyester thread is made for machine sewing, and I do everything by hand, the piecing and the quilting. Machine-sewing thread is often not well suited for hand sewing.
Furthermore, my mother always said that for something that I meant to last long, I should never use a thread with a fiber that was stronger than the fabric's fiber.

In her book about handquilting 'That Perfect Stitch', Roxanne McElroy says something alike:
'My teacher told me that if we were to make a garment of polyester, we must use polyester thread. (...same for silk, cotton....) If you were to make a garment out of polyester and sew it with cotton thread, you would constantly have to re-sew your seams, because the friction of movement would rub one fiber againt the other. The polyester would win every time because it is stronger. If you made a garment of cotton and sewed it with polyester thread, the polyester thread would cut the cotton fiber.
In looking at older quilts, I have seen evidence that this "balance of power" between fabric and thread is very imporetant. Quilts made as recently as the 1950s, when polyester first became popular, are already beginning to come bac to quilt shops for repairs. "

She continues/
"think of the reasons you are making your quilt before you choose your thread. If it is a quilt to fit in with a room decor that might change in a few years anyway, or if it is for a child who will love it to death, matching th thread to the fabric may not be important to you. But if you are making a heirloop quilt or want you quilt to have maximum longevity, take care with thread selection."

Jinny Beyer too, in 'Quilt making by Hand', suggests to use 100% cotton.

And I admit, I'm not such a good quilter that I can hope my quilts will become heirloom, especcially since I'm in Europe, where quilting isn't such a rich tradition as in the States. But because all my quilts are 100% made by hand, I do want to give them maximum longivety, although that may sound a bit vain...