Date: 4/30/12 7:35 PM
If the fabric pieces are cut on the bias, then the interface pieces should also be cut on the bias. Since all armscye curves are on biases, Those facings get cut on bias, even if it appears that the blouse piece is cut on straight grain.
Also, don't slouch the grain degree, or the two pieces will relax and stretch and shrink at different amounts, and you will get puckering, wrinkling, and eventually, a very poor garment hang that will get worse with each laundering or cleaning..
Pfaff 1471, janome 8050, bernina 830, Pfaff Passport 2.0; sergers singer quantum lock 5, baby lock protege, pfaff 794