Draping circular (/flared) skirt (IV): Preparing-the-toile saga

This post comes late as it turned into my biggest geometrical challenge of the last several years. The instructions in the book I am using were simply wrong. Not a big deal if you have some knowledge of draping and sewing, but... 

Instructions

To prepare the toile, the book suggests preparing the toile as shown on one of the illustrations (I have recreated it to show what didn't work out):

Suggested width of the fabric should be +/- 150 cm (60”), and the length about 1m (40”).

(Warning: Please read the entire post before you follow the instructions.) There are only two steps for preparing the toile:

1. “In the middle of the piece of fabric indicate in red the vertical grain line and the horizontal grain line.” – This step was clear to me.

2. “ Divide the two halves lengthwise and make diagonal lines between the two lines. This is the true bias”

This is where my problems started. According to the illustration in the book, fabric width is divided into four equal parts: 

150cm : 4 = 37.5cm

or in inches

60” : 4 = 15”

Similarly, the length is divided into two equal parts:

100cm : 2 = 50cm

in inches:

40” : 2 = 20”

Now, if you look at the illustration, after you have marked your lengthwise and crosswise grains, and the additional two lengthwise lines in the step 2, you will end up with eight equal rectangles. The problem is that the diagonals drawn this way are NOT on the true bias.

True bias runs on “an angle of 45º drawn on the selvage” (quoting the book). Diagonals we got on the muslin do not run on 45º, because, and it’s a simple geometry lesson, to divide a 90º angle of a ‘quadrilateral’ (sorry for the terminology) into two equal angles, it has to have two equal adjacent sides. In other words it needs to be a square.

However, if you followed the book instructions, you ended up with a 15” x 20” rectangle. The angles at which diagonals are marked are 36º and 54º, far from true bias.

What did I do wrong?

I made very stupid thing - I tried to turn rectangles into squares by increasing the width without realizing it. It started with the muslin fabric, which was only 44” wide. I cut two 40" (100 cm) long pieces and stitched them together along the selvage, ending up with appr. 86” wide fabric.

Being used to metric system, I didn’t think about how centimetres translate into my 60” wide fashion fabric, so I went on measuring one meter along the seam joining two pieces of muslin together (my lengthwise grain). I divided that one meter into twice 50cm and drew a line along the crosswise grain (folding fabric in half helps)


I have already figured out the problem with instructions and measured twice 50 cm to the left and twice to the right.  (How stupid, I didn’t add up, because then I would know that I am ending up with 2m width – 50cm wider than my fashion fabric)

So, I continued and marked the diagonals on the muslin, drawing them through the corners of squares I got. Perfectly true bias, at 45º

The last things I did, I made small 2” (5cm) markings along the first 12” (30 cm) on the top of fabric. Once you start draping, you will need to cut along this line for the first 15or 20 cm to create some flare. The deeper you cut, the bigger the flare be. 

Great, the toile is marked! And, you know what? I haven’t noticed the mistake until I was about to cut the fashion fabric, with all the draping behind me.  I will come back to it in my next post. 

So, what is the solution?

If you are working with 60” fabric, make marking as on the following illustration:

Note, how the diagonals cross the rectangle forming four equally sided (15" for each side) triangles. Now, they mark the true bias.  

Before you cut the fabric: Limitations and advantages of this design

I will write more on this, but first thing that comes to my mind and I would like to share before anyone else proceeds on this project, is that with this design you won’t achieve very wide flare unless you sacrifice the length (or you are making a skirt for a child).  But this design is great for prints –you have only one seam to match... 

please, stay tuned in for the continuation of the skirt saga