So if I understand you are talking about Bolstered Ward. (My like new favorite spell that they haven't added to the game! Curse you KI! JK, but I would like it added as a trainable spell.....) Anyway what this does is similar to a potent trap or a Sharpened Blade, but for Shields.
How it works if you click on it, other spells will grey out except for shields in your hand. when you click on a shield a new card will be created. So if for example you have a -50% tower shield and a Bolstered Ward Item card when you use the Bolstered Ward on the Tower Shield the it goes from -50% to -60%! It's amazing and is also stackable! Hopefully that helps and I really hope that KI adds Bolstered Ward to the Arcanum's list of possible spells to train!!!
please help thanks