What would be the best way to create a diamond pattern on a cake iced in buttercream? I looked for a diamond impression mat, but our local stores didn't have one.
shishkabob skewers. Press those into chilled and/or crusted buttercream.
You can use a ruler or a quilter (a diamond metal thingy) to make the quilting patterns. Hope that helps!
By the way, WELCOME to CC -- better known as your new addiction!!
If you're willing to purchase on-line...Sharon (sugarshack) sells a diamond mat for buttercream at a great price: http://www.sugaredproductions.com/Decorating_Supplies.php
The skewers worked great! Thanks for the tip.