If the frost top is to be contained to a particular section of the entire top do you use heat wire to control it. This idea has been sugested to me and it was adopted for production but wasn't sure it was needed.
We were commisioned to build a granite top unit. One piece of stone 10 feet long, but only a 2 foot by 3 foot section to get frosted. To insure the frost stayed within the outline we installed a heat wire ( similar to a mullion heater, around the perimeter. It works but didnt think it nessesary. Never used it I gather. As far as the Cut-in / Cut-out I figured it would by trial by ice. Ken