Remember I was talking about darts in stretch fabrics yesterday and how people don't think they're important? Besides not wanting to use them simply because there's one less line to sew, usually the first justification is that the fabric is forgiving enough to stretch around even the largest breast. Well no it isn't ... a B to C maybe (and I'll still dart for that so I have control over tension),above a D and really you're squishing the breast into an unflattering shape.
The second justification from the smarter sewists is that little pimple you see at the end of a dart which they say is where the sewing runs off the end. Well ok the stitch does run off the end, but that's not at all the reason for the pimple.
I love moments like these ... because I know in a minute you're going to go away with an ohhhhh expression and life will be changed forever..
Those pimples are quite common in non stretch too, but normally they're subdued (not pronounced as they are in swimwear). They're due to straight darts creating a corner same as non-stretch ... but that's not all ... here's the cool bit ... that corner sits proud with absolutely no tension in it and all the fabric tension around it pulls away in an attempt to balance everything out but can't go all the way to the point so it creates a gradient up to point that isn't uniform ... the body pushes back into that gradient and you end up with a little mini volcano ... it's subtle but you can measure it by drawing even circles on the fabric before you sew it and measure them after ... the last photo shows the gradient from a straight dart in a triangle top and the photo on the left is my two dart triangle pattern piece..
You can reduce this pimple effect by creating a curved dart instead of a straight one ... the middle photo is exactly the same pattern piece but with curved darts. The right photo shows how the tension doesn't drop all the way to zero at the point so there's almost no visible pimple ... and the affected area is also much less (this is not the real pattern piece but an illustration only)
Now when we're talking about a larger bust and we're trying to cup it from both sides there is left to right strain in the finished garment ... in the case of the straight darts, that strain would go through two zero ease areas and change the shape of the bust to something having an edge along that line (the folded line in the first photo).The curved darts don't drop to zero so don't really have this problem and keep the designed shape.
Two curved darts, spaced evenly along the underbust line ... massive difference to the overall fit, shape and support of even a simple triangle ... now is that worth the effort or not?
My Buxom Bosom Block already has the double curved darts built in ...