Thanks, everyone, for the comments. I found this article online that might be of interest:
http://quiltersreview.com/index.php/...t-to-the-test/
The table she links to does show SewArt as being the most invisible, so I'm bummed that it is no longer being manufactured. May have to stick with my YLI. I do have some Sulky on hand, and also some Superior mono-poly, so I think I'll conduct my own comparison test to see if I really might want to change.
Thanks for the info about Superior's matte finish mono-poly! Think I'll order a spool of that and add it to my comparison testing.
Regarding the smoke color, I do have this in YLI also. It's too dark to use on a light colored background, and anyway the shine is very similar to the clear.
There is conflicting information about nylon monofilament versus polyester. Theoretically poly should be better, but I have never had a problem with the YLI monofilament. It has never melted under my hot iron, and Harriet Hargrave swears it has not turned yellow or brittle (and many of her quilts must be quite old by now -- 20 years or so?).
If I did hand applique I would definitely try 100wt silk thread, but it sounds as if it shows up too much to work well for invisible machine applique. At least I haven't found any articles on the net that explain that it works well for that technique.
I'm so glad I started this thread (no pun intended
). Have learned a lot!
Edit: Rats!!! Just checked the Superior website and they are out-of-stock of the clear matte-finish polyester.