When transferring drat lines from your sewing patterns to the corresponding fabric pieces, you will find yourself in a bit of a complex situation if your pattern as been cut on fold or double cut. In this instance, the dart lines will have to be transferred to wrong side of both fabric pieces at exactly the same corresponding location, as accurately as possible.
As a reminder, when cutting double cut or cut on fold patterns, the fabric layer should be folded such that fabric face sides are touching. Doing so will ensure that all transferred line, particularly drat lines, are safely transferred to the wrong side of the fabric pieces. Not only does this protect the fabric's right side, it also facilitates the dart folding and stitching process, considering that darts are sewn form the garment's wrong side.
If you prefer to use a fabric pencil and tailor's chalk, you can use the following techniques to transfer dart lines to both fabric layers prior to separating the pinned pattern:
1. Before unpinning and separating the paper pattern from the cut fabric layers, insert a few pins directly in top of the dart lines, catching the paper pattern and two fabric layers underneath. Insert another pin directly through the dart point and both fabric layers underneath.
2. Flip the pinned pattern on the other side to expose the pin marks. If your fabric has been folded and cut correctly (face sides touching), the pin marks should correspond to the wrong side of the bottom fabric layer. Transfer the dash lines and dart point created by the pins to mark the general shape of the dart.
3. Now for the tricky part: You will have to transfer the same exact dart to the wrong side of the other (top) fabric layer. The wrong surface of this fabric piece sis located right underneath the paper pattern. A way you could transfer the pin marks to this area is by unpinning the whole pattern at the bottom and marking the dart pin locations as you reach them. Remove each dart pin as you mark until the entire dart is transferred with dash lines. Don't forget the dart vanishing point!
A more simple way to transfer dart lines to the wrong side of the top fabric layer is by removing the dart pins and perforating a few areas along each dart line and at the dart vanishing point using a pin.
You can then use your fabrci pensil to mark at each pieerced location directly on top of the fabrci layer underneath. As a result you shoudl have multiple points that form the general shape of teh dart. It is important to keep the pattern as flat and smooth as possibel during this transfeer process.
4. Now that you have the darts marked on teh worng side of both fabrcic layers, you can confidently connect the dots using a ruler and your fabrci pencil (or tailor's chalk). Draw all three line sstartinga the dart's vanishing point and ending at each individual notch along the fabrci edge.
You can use tailors chalk insteda of a fabrci/quilting pencil, espcially when marking on thicker. motre textured fabrics. The cjpice is all yours as long as the marking tools you use can be safely removed with teh garment's first wash cycle.