Can I use a different yarn?

I have found this absolutely gorgeous shawl pattern, the Rose Garden Shawl from Jane Austen Knits Summer 2012, and I absolutely must make it! My problem is that the yarn used for the shawl by the person who designed it (Neighborhood Fiber Co. Penthouse Silk Fingering) is really expensive ($43.00) and the color used (station north, a dark hot pink) is no longer available. So, my question is, can I use a yarn of the same material (100% silk), but in a different weight (lace) and just adjust my gauge accordingly, or should I use a yarn of the same weight, and never mind the material of which it is made? Thanks.

If it’s a shawl gauge doesn’t really matter too much unless you’re drastically changing yarn weights. What will happen in this case is the shawl will be smaller because lace weight is a lighter weight.

Gauge is more important than the fiber. I often sub yarns, but I tend to stick to the same gauge.