I bought a pump bottle of Stiffen Stuff at Michaels and loved how it worked on crocheted snowflakes. I didn't have a board to stretch & pin so just laid the snowflake on plastic wrap & sprayed, straightening if needed.

I don't stiffen bookmarks and only stiffen doilies when necessary. Certain ruffled doilies or those that have a portion that need to stand up do require it. I've used liquid starch a bit diluted with water.

Thanks for your responses.