I would think brass would turn the fur different colors if it wasn't laquered. Chances are a good, more expensive, brass tag would be laquered so I wouldn't worry.

I used to have Allen wear a collar all the time. I finally took it off him a few months ago because I felt bad he was the only one wearing a collar. Pouncer was the great escape artist and got out of ANY collar I put on him. Ten minutes after I found it and replaced it on his neck, it was on the floor somewhere I finally gave up knowing he was more determined to be out of it than I was to keep him in it. I have plans on getting him and the kittens microchipped once I get a job. Hopefully sometime before spring. Are your kitties microchipped?