[size=14]The buttering over would be done on a 'pattern'.
For example: Griswold and Wagner and others, would alter an original pattern by filling in the previous letters/numbers/ logo with a hard material, and then redo the 'new' markings that were desired. Patterns were a big 'expense', so they would alter an existing 'pattern'. With continued use of the 'modified patterns' making impressions in the sand molds, the sand would abrade those "buttered" over areas, over time, and hence, the 'ghosties' would emerge (previous markings).
If a Skillet was used to produce a Pattern, the same principle would apply, and the finished product would be 'smaller' than the original skillet used to make the 'pattern'. :) [/size]