Step by step instructions: https://www.littlethings.com/lace-window-treatment
Hi Dawn: Here are a couple of sites that tell you exactly how to do this. Pick your favourite:
Hi Dawn. Begin by cutting your lace to exactly fit the window that you're covering. Then mix equal parts of cornstarch and cold water. Mix well until the cornstarch dissolves. Then add another equal part of boiling water . Paint this mixture on the window. with a clean paint brush. Smooth your cut piece of lace onto the corn starched window. Then paint more of the mixture on top of the lace. Good luck Dawn.
Thank you, Dawn. I've never heard of this but I'm already planning to put it into action.