Make Baby
Buttons are usable as they are made of acrylic material. Acid-free would refer to items that are not treated with acid in the process i.e. our newspapers are acid-treated and has got lignin content, thus it turns yellow really easily.
So in terms of lace/threads, the I believe the dyes usually used are not acidic but do correct me if I'm wrong. But end of the day, if you like threads, I always go for those DMC (I think that's the brand) used in cross-stitching), laces will buy from either local stores or textile centre.
End of the day, what's with the fuss of using acid-free products...so that we hope that our craftwork would be of archival quality and lasts us for ages to come. Till when we are old and greyed with hair and carrying our grandchildren.
If you notice that our parent's picture albums or those sticky/tacky albums we got easily from Popular bookstore, and how easily those sticky albums turn yellow? That's because the type of glue is not acid-free, this in turn will destroy and affect your photos. That had happened to a few of my albums and I desperately salvaged those photos that doesn't have negatives anymore by taking them out of those albums. And this is within 5 years!!!
So in SB, we try to look out for labels like "acid-free", "lignin-free", "archival quality of archival safe" products. More so for adhesives that is in direct contact with the photos that we use. This slows down the aging process of our keepsakes from yellowing.
So example for felts sold at the LSS, produced by those SB manufacturers, why we buy them coz most of them come in adhesive backing(especially those intricate felt border designs), and we trust that these SB manufacturers uses acid-free adhesive on them.
However, with a bulk of our SB layouts being acid-free, alot of scrapbook artists have moved on to mix media art....using various types of materials into their craft i.e. corrugated board, etc etc.
So end of the day, it's a personal choice whether we want our stuff to be acid-free or not. For me, a bulk of my LOs are using acid-free paper, cardstock, gluetape, archival safe pens....
Hope this helps....and I hope I'm answering your question directly.... hahaha