Is stitching with thread archival safe for your pictures?

I am really into the preservation of my photographs more so than the addition of adornments to make my page look good so normally I only scrap with acid free/lignan free paper and stickers. But I really like the look of the quilted paper layouts using a sewing machine and thread. But I am worried the thread will have acid in it. I have no idea how to find out if it does. Does anyone know?