I am making boxes for the Grandkids and want to put their initials on the top of the box. I will be cutting V90 or 60 initials into the top. The wood is pine. What I’d like to see when finished is a a box with cherry stain and coated with a poly coat. Would like to fill the letters with WHITE SOMETHING and not have it absorb the stain and can be sanded. Any ideas… Thanks