I use grout whitener to refresh the letter or logo on a vulcanite stem. My procedure is to get the oxidation off the stem and return it to jet black. The grooves of the stamping must be cleaned out under magnification using dental picks and probes. The job usually involves deepening the recesses with the same tools. Shake the pen for 2 minutes and apply a small amount over the area. After setting up for a minute I  use a toothpick to roll across the area and soaking up the excess liquid, leaving the grooves filled. After hardening awhile, i can buff it with carnuba wax to protect and seal the work. I prefer the Miracle grout pen over the Rustoleum brand. I find the Rustoleum is too watery.

Thanks for looking!