I printed out a character in HIPS the other day. Yesterday I experimented with acetone smoothing, and I can absolutely verify that HIPS smooths BEAUTIFULLY and quickly in acetone vapor. It actually begins to smooth as soon as you put it in the vapors. It is much faster than ABS.
BUT as the picture I uploaded shows, after the print “dried” it developed these odd little spots all over it. They did not appear until well after the print felt dry (it actually felt dry minutes after removing it from the acetone bath). I am using HIPS I got from Lulzbot/Aleph, and it is the gray filament. It looks like the pigment is separating somehow.
The natural colored ABS I smoothed at the same time did not develop these spots.
Anyone have any ideas why this happened?