The Gathering Foot and Elastic Shirring

  Y yo que no sabía como usar el hilo elástico, ahora sí aprendí

Using A Vintage Sewing Machine: The Gathering Foot and Elastic Shirring

 http://susanscloches.blogspot.com/2010/05/using-vintage-sewing-machine-gathering_19.html

The Gathering Foot can be used with elastic thread to make stretchable shirring.

The elastic thread must be used on the bobbin. To wind the elastic thread onto the bobbin you must do it by hand; you can't run elastic thread through the bobbin winder. Don't stretch the elastic while winding it on the bobbin but also don't have it so loose it's floppy. You can hold the bobbin in your hand and loosely wind the thread around it. I find it easiest to stick the bobbin onto a pencil, put the elastic thread on the spool holder for bobbin winding, and twist the pencil to wind the thread as it comes between my fingers loosely. I pull the elastic thread off the spool when I feel it stretch as I'm winding so it's slack and not pulling. You can see this in the next (over bright) photo where the thread I'm winding is coming off the spool and lying on my sewing table as I'm twisting the pencil.