I recently had an enlightening converstion with fellow vintage knitter, blogger and instagramer Theodora. I mentioned using the 2 ply Jamieson and Smith yarn, which I have used several times as they have such a great range of colours at my local yarn shop (Prick Your Finger in Bethnal Green), even though it is a bit itchy. She told me it won’t knit to the true 3 ply size and your garment will come out bigger, and I had an “a-ha!” moment, realising that by using this yarn I had accidentally made a couple of sweaters exactly the bigger bust size I needed. Looking at their website, it calls it 2 ply Jumper yarn and says you can use it for knitting vintage patterns which call for 4 ply. Has anyone tried the 2 ply lace weight? The J & S website says that this is suitable for vintage patterns asking for 3 ply.
I just purchased some of the same Jamieson and Smith yarn for a vintage knit pattern and was quietly hoping it might knit up a little bigger, just stumbled on your site and happened to read this post and discovered that yes, it may well do!