I always get a kick out of cruising the UFO's on Ravelry and seeing, "I'm finished except for the seaming." ROFLMAO! Honey, you are nowhere near finished, but you are at the fun part.
Call me a freak, but I really do enjoy seaming. *Sometimes I put it off, and I have no clue why. I guess it's one of those knitting chores that you're supposed to hate--I hear that all the time. But really, seaming is the icing on the cake, the cherry on the sundae, the lime in the tequila. It's the make or break part of any knitted and seamed garment, crochet too. Even if the pieces--body, sleeves, collar--are knitted to perfection, if the seaming is crap, all your hard work just ends up looking like, well, crap. No pressure, eh?
Here's my Ribby Cardi, main pieces knitted, and laid out to form the sweater:
No, I am nowhere near finished, because I still need to weave in all the yarn ends, seam the sleeves and body, attach the sleeves to the body, knit on a collar, pick up stitches on the fronts for the zipper bands, then add an i-cord bind-off for the zipper bands and along the collar, then baste and sew in the zipper. But before I do all that, I need to steam the edges flat. If this were a wool yarn, I'd go ahead and block all the pieces first, but since it's a cotton blend that's just going to end up being tossed in the washer and dryer, I'm not going to bother. But I do want the edges nice and flat for seaming. This is where my little-used iron comes in handy.
The sleeve edge on the right hasn't been steamed flat. Notice how it curls. The sleeve edge on the left has been steamed and is nice and flat, making it very easy to see the edge stitch and the one next to it. Between these two stitches is where you'll find the horizontal bar that's picked up for mattress stitch seaming.
Since this particular yarn--Berroco Weekend--is comprised of four plies, I'm going to divide my seaming yarn in half, to keep the seam bulk to a minimum. Obviously you can't do this with a single ply yarn. In that case, I'd consider seaming with a smaller gauge yarn in a color that closely matches the garment.
As for steaming the seams, yes, I do use an iron, and no, I'm not concerned about killing this yarn even though it is mostly acrylic. I don't press down on any spot for more than a second or two, but the iron does touch the yarn and I do use the steam setting. I find that it takes a lot of work to actually kill acrylic--I really have to use force and show it who's the boss. For this sweater, however, I'm not going to use the iron on anything but the seams and edges. There's no sense tempting fate.
*Yes, I started this sweater over a year ago--delayed gratification!