How do I get this effect on the side of a cake?  If it is impression mat, which one?

AThat looks like piping to me, also looks like a henna design/pattern.

I agree it's piping.  I was wondering if it started with an impression.  It's so uniform!  I don't know that I could do all that free hand!  I like the idea of searching for henna impression.  I've been looking under "lace" and haven't been able to find.

AYep it's very intricate, I also do henna designs so the pattern looks familiar. You should try it, it's fun to do although tiring!!

I am revisiting this thread.  I now do not believe this is hand piped without a pattern.  I saw several cakes on pinterest that had this exact design.  It has to come from a pattern.  Can anyone help me find the mold or stencil??  I'm not having any luck.

not exact--but you (i) could get there from here:

http://www.globalsugarart.com/jacobean-style-floral-applique-cutters-by-jem-cutters-p-18908.html

and just fill in all the spaces in between with dots and scrolls etc.

this diagram gives the dimensions:

http://www.sugaredproductions.com/shop/search.php?search_query=jacobean&x=0&y=0

in fact--if you go here and click open the thumbnail on the right--it gets you closer & closer

http://www.sugaredproductions.com/shop/products.php?product=Jacobean-Lace-Set

when you overpipe you can pull the design any which way you want--kwim

Googled "henna stencils for cakes" and yielded the following:

https://www.google.com/search?q=henna+stencils+for+cakes&tbm=isch&tbo=u&source=univ&sa=X&ei=esP2Uqz4FuWbygG5xYH4BA&sqi=2&ved=0CDsQsAQ&biw=1250&bih=538&dpr=0.98

There's got to be a link in there that will help.