Done on 8 x 5 unlined index cards folded in half (use a pencil on it’s side to go over the crease to make it crisp)
I fold the card before I do the rubbing to plan for space so I know exactly where the front of the card will actually be.
I found this metal Christmas decoration at the consignment shop. I actually bought it because of the raised scroll-work.

Practice off to the side to figure out which part of the scrollwork you like and how it turns out as you do the rubbing. Also, rubbing the back gives it a bit of a different look.

Rubbings with colored pencil work best if the pencil is sharpened but not the “first use” of the freshly sharpened pencil. Dull it a little bit on another piece of paper, and be sure to hold the pencil more sideways than straight up and down as you go over the item you are rubbing over.
I usually pack six cards and corresponding invitation envelopes in a package as part of a gift basket or gift bag.