Several years ago I attended a wonderful class on burning silk. In this class we used candles and a quick in/out motion to burn the edges. We made lovely butterfly wings that we attached to fabric.
Although this method worked great, I've found a wonderful substitute that many of you may already use. For those who haven't heard of the Creative Textile Tool by Walnut Hollow, I would invite you to visit their website and take a look at the different tools they offer.
I have the Creative Versa-Tool which does an equally great job of burning silk. I enjoy using graphics in my crazy quilt blocks, purses and needle cases. Burning the edges gives a vintage look to the graphic and also prevents fraying.
I also love the effect of burning my silk leaves. The leaves on this large rose have been burned on the edges.
These tools serve a variety of uses and probably many that haven't been thought of yet.
Wood Hollow offers a great product at a reasonable price.