In pattern drafting, you often want to add fullness to the shape of a pattern piece:
The CORRECT way to add fullness is from WITHIN the pattern piece.
The INCORRECT way is to tack on more to the OUTSIDE the pattern piece.
Adding fullness WITHIN the pattern piece is called “Slash-and-Spread”. The reason it works is because it changes the shape while simultaneously keeping smooth edges. Imagine the difference between blowing up a balloon (changing the shape from within) versus patting clay or Play-Doh onto the outside (lumpy and distorted).
Can you tell what is wrong with this picture? (It’s not a high school math assignment, it’s a pattern piece.)
This is how to make the A-line skirt portion of a VERY cute pdf dress pattern released this week. (Seriously, the cuteness is in the bodice and you need to buy the pattern to see that. I’m only showing the one pattern piece of the skirt, which you could guess from the tester photos.) The left vertical is the center-front/back, the top horizontal is the waist, the bottom horizontal is the hem, and the diagonal is the side-seam. A measurement chart is included for you to draft your pattern piece. So it’s a basic rectangle, with fullness added as a triangle on to the OUTSIDE of the rectangle, making a trapezoid.
I’ve seen this shape so many times in indie-designer PDFs and it bothers me every time. So I’m going to explain WHY this is an incorrect way to add fullness to a skirt, and then HOW to add fullness correctly.
WHY this is incorrect: Adding fullness by tacking on to the OUTSIDE of a pattern piece causes 2 problems:
Fit (the shape is now wrong)
Trueing (lumpy uneven edges)
FIT: An extreme example of fitting problems caused by tacking on extra fullness to the OUTSIDE of the pattern piece is shown in this post:
The fullness added to the sides does nothing to affect the fit (fullness) of the garment body, it’s simply an appendage. The A-line skirt example is far less extreme, yet it still follows the same principle. Adding fullness to the OUTSIDE of a straight skirt does not create a proper A-line. Take a look at the drafted pattern piece in a size toddler 2 :
1. The fullness flares the sides, but not the front or back of the skirt
2. The skirt length is longer on the sides then on center-front and center-back (okay that IS high-school math: the diagonal of the trapezoid is longer)
Those are the FITTING problems, but now look at the TRUEING issue. “Trueing” is the process of checking that when darts and seams are stitched, the resulting shape is smooth, so that you can proceed to the next step in construction. For example, skirt pattern pieces should have 90-degree right angles at the bottom corner of the side-seams, so that when the front is stitched to the back, the result is a 180-degree straight line, suitable for hemming. But in the case of this A-line skirt, the trapezoidal shape means you cannot get the 180-degree line that you need. Instead it creates a triangle dip that doesn’t fold up properly for a hem:
You are forced to fuss with a strange hem, or else trim off the triangle bit, to create the 90-degree angles front and back, resulting in the 180-degree straight line you need for the hem. In other words, YOU need to true this pattern, because it wasn’t done for you in the drafting process.
But you still haven’t solved the problem of the fullness being all at the side-seam and not within the body of the skirt itself. This is why the pattern should have been drafted NOT by tacking on to the outsides, but rather by “Slashing-and-Spreading” from the inside. (I’ve shown S&S in this post for a flared dress and this post for a back pant rise).
HOW to add fullness correctly:
SLASH-and-SPREAD: Let’s take the same pattern piece and chop off the fullness tacked onto the sides that was supposed to create the A-line shape, so that we can put it in the correct place:
Now take the basic skirt block, slash it from hem up to waist from the INSIDE. Then cut up the triangle that was just removed into the the same number of pieces as the slashes:
Replace the fullness that was cut off from the OUTSIDE, and put it INSIDE the body:
The resulting pattern piece has a gently curved hem, and consistent length everywhere. Two things happen automatically:
The fullness is now added throughout the body, not just tacked onto the sides
The side-seams are instantly trued! When you stitch front to back at the side-seams, the result will be a 180-degree straight line, ready to be hemmed without trimming off any triangle.
You can use the Slash-and-Spread method when drafting your own patterns, or to add fullness to existing patterns, or to correct weird pattern shapes…like trapezoids.
PS: added for clarification: Slash-and-Spread will also correct the waistline. The original straight-across pattern piece creates a Vee-shaped “dip” at the waist on the side-seams:
After Slash-and-Spread, the waist will have the same gentle curve as the hem, the Vee will disappear and the corners of the pattern at waist-side-seam will be “trued”.