1 strand or 2, it's all in what kind of coverage you like.  Personally, I think 2 strands over 1 on 25ct (what HAED recommends) is too bulky.  But 1 strand over 1 on 25ct is almost not enough.  So, I'd probably go 1 strand over 1 on 28ct instead.  but if you like to tent stitch (basically stitch the whole thing in half stitches), then I'd probably use 2 strands.  But you just need to get a piece of fabric and do some test stitching to find out what count/# of strands you like. 

Vanessa

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Mira UFOs: White Christmas (color conversion), Rose of Sharon (over 1), Autumn Maiden (from Maidens II), Athena, Poppy (over 1), and 2007 Christmas Tree, Angel of the New Dawn, Ella,Spring Topiary Fairy (left side).