I don't usually sift my sugar for buttercream, but found a tip to run it through my food processor to break up the lumps.
Tried it and my buttercream seemed the same to me. No lumps.
It sure made it easier for sifting to make fondant, though!
To answer the questions.....
I always sift the icing sugar it definately gets rid of the lumps and will make the icing much smoother.
You will need a sift with slightly bigger holes to sift with else the whole sifting process will become a nightmare.
Good luck
I sift each and every bag since I found some rather large sugar crystals while icing a wedding cake bake in April with Domino sugar. I'm just glad that I felt them with the spatula and not someone biting into to them. It's worth the little extra effort. Pam from Bama
I never sift, I used to until I found out if there is lumps then just use a whisk, the 10 x is already sifted for one....it's just a step that I find doesn't help me or hurt me....I also add all my liquid to my shortening and emulsions and whip then I add my whole bag of PS and just let it mix...it stays smooth and no air bubbles.
I don't sift either. I've tried it and have not noticed much difference and definitely not enough difference to make up for the time and mess . If I need my icing to be particularly smooth (ex: with the grass tip - clogs easily if there are any lumps), I mix in some piping gel and that seems to do the trick.
To answer the questions.....
I always sift the icing sugar it definately gets rid of the lumps and will make the icing much smoother.
You will need a sift with slightly bigger holes to sift with else the whole sifting process will become a nightmare.
Good luck
Same here. I ALWAYS sift my sugar. I finally realized that I didn't need to do it if the icing is ONLY for covering the cake, not for decorating.
I was thinking its like a colunder(spelling)I am soooooooo clueless 
not a colander. I seive is what some people use. It has a metal ring from which a handle extends and in that metal ring is a semi-sphere of mesh. People shimmy them or use a spoon to agitate the contents which pass through the screen. An actual sifter is a cylinder of metal with a handle. Inside the metal is one or two mesh screens. A mechanism of one kind or another agitates the contents of the sifter, allowing it to pass through the screens.
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