For all gold vessels with a protective lacquer, I recommend using a cloth made of 100% cotton to remove fingerprints, residue, etc. Try to avoid using cloths that contain a blended fabric (especially polyester), as these will potentially scratch the finish. Also, NEVER apply Brasso or any other chemical to the. Doing so will remove the protective finish and will cause the piece to tarnish more quickly.
I recently had the pleasure of assisting a customer with an Ostensoria purchase for the permanent Diaconate program in the Archdiocese of Los Angeles. After presenting the customer with several models and styles, they decided to go with style FCZ M-575 from the F.C Ziegler Company. Upon receiving the Ostensorioum a few days later, the customer called to let me know how beautiful the piece was. The customer also asked me about best practices/recommendations in regards to maintaining the Ostensorium's beauty.